Crystal vibration element, and crystal vibrator equipped with crystal vibration element

ABSTRACT

A crystal vibration element that includes a crystal piece that has a prescribed crystal orientation, and a first direction and a second direction in a plan view thereof; and excitation electrodes that are respectively provided on front and rear surfaces of the crystal piece in order to excite a thickness shear vibration in the crystal piece upon application of an alternating electric field. A vibration distribution of the crystal piece has a vibration region that extends in a band-like shape in the second direction of the crystal piece and non-vibration regions that are adjacent to opposed sides of the vibration region in the first direction of the crystal piece.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International applicationNo. PCT/JP2016/079920, filed Oct. 7, 2016, which claims priority toJapanese Patent Application No. 2015-200232, filed Oct. 8, 2015,Japanese Patent Application No. 2016-059077, filed Mar. 23, 2016, andJapanese Patent Application No. 2016-089765, filed Apr. 27, 2016, theentire contents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a crystal vibration element and to acrystal vibrator.

BACKGROUND OF THE INVENTION

Crystal vibrators in which a thickness shear vibration is employed as amain vibration are widely used as the signal source of a referencesignal used in oscillation devices, band pass filters and so on.

For example, Patent Document 1 discloses a piezoelectric vibrationelement that is held inside the sealed internal space of a holder andthat is provided with excitation electrodes close to a central part of apiezoelectric plate. The vibration distribution of a thickness shearvibration in this piezoelectric vibration element spreads in the form ofsubstantially concentric circles from a central part of thepiezoelectric plate toward the outside of the piezoelectric plate, andthe vibrational displacement of the piezoelectric plate becomes smaller,the closer the vibration is to the outside of the piezoelectric plate.Patent Document 2 discloses a configuration that suppresses degradationof characteristics such as a crystal impedance (hereafter, “CI”) valuethat is caused by obstruction of the vibration of a vibration portionthat occurs together with flowing out of a fixing member such as anadhesive by making the dimensions of a mesa-type piezoelectric vibrationpiece satisfy a prescribed relational formula. Furthermore, PatentDocuments 3 and 4 disclose configurations in which excitation electrodesare formed on main surfaces of a crystal piece, which has a long thinshape, so as to extend up to long sides of the crystal piece.

Patent Document 1: Japanese Patent No. 4458203

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2013-102472

Patent Document 3: Japanese Examined Patent Application Publication No.56-36814

Patent Document 4: Japanese Unexamined Patent Application PublicationNo. 2001-7677

SUMMARY OF THE INVENTION

However, in the case of a piezoelectric vibration element having asubstantially concentric circular vibration distribution as disclosed inPatent Document 1, a region where the displacement caused by thevibration is small or non-existent is adjacent to the outside of thesubstantially concentric circles in the piezoelectric plate. Therefore,it may not be possible to obtain good vibration characteristics in that,for example, a drive level dependence (hereafter “DLD”) characteristicis degraded, and the CI value is high and the value of the capacitanceratio γ is large due to the width of the vibration region being smallcompared with the width of the crystal piece.

Furthermore, prevention of vibration leakage to the main vibration maynot be sufficient in the configurations disclosed in Patent Documents 3and 4.

The present invention was made in light of the above-describedcircumstances, and it is an object thereof to provide a crystal vibratorthat can realize good vibration characteristics.

A crystal vibration element according to an embodiment of the presentinvention includes: a crystal piece that has a prescribed crystalorientation, and a first direction and a second direction in a plan viewthereof; and excitation electrodes that are respectively provided on afront surface and a rear surface of the crystal piece in order to excitea thickness shear vibration having a main vibration in the firstdirection in the crystal piece upon applying an alternating electricfield. A vibration distribution of the crystal piece in which athickness shear vibration is a main vibration has a vibration regionthat extends in a band-like shape in the second direction of the crystalpiece and non-vibration regions that are adjacent to opposed sides ofthe vibration region in the first direction of the crystal piece.

A crystal vibration element according to another embodiment of thepresent invention includes: an AT-cut crystal piece having a firstdirection and a second direction in a plan view thereof; and excitationelectrodes that are provided on a front surface and a rear surface ofthe crystal piece so as to face each other. A vibration distribution ofa thickness shear vibration having a main vibration in the firstdirection has two amplitude nodes that extend so as to cross two sidesof the crystal piece that face each other in the second direction andthat are provided so as face each other with a distance therebetween inthe first direction, and an amplitude antinode of a vibration regionthat is provided at a position interposed between the two nodes.

A crystal vibration element according to another embodiment of thepresent invention includes: a crystal piece that has a prescribedcrystal orientation, and a first direction and a second direction in aplan view thereof; and excitation electrodes that are respectivelyprovided on a front surface and a rear surface of the crystal piece sothat the crystal piece has a vibration region that is located in acentral portion in the first direction and that vibrates with at least athickness shear vibration, and non-vibration regions that interposedtherebetween both sides of the vibration region in the first direction.Boundaries between the vibration region and the non-vibration regionsconnect two sides of the crystal piece, which extend in the firstdirection and face each other in the second direction, to each other,and extend in a wave-like shape in the second direction.

A crystal vibration element according to another embodiment of thepresent invention is a crystal vibration element in which a thicknessshear vibration is a main vibration. The crystal vibration elementincludes: a crystal piece that has rectangular front and rear mainsurfaces; and rectangular excitation electrodes that are respectivelyformed on the main surfaces of the crystal piece. Long sides of theexcitation electrodes are parallel to opposing long sides of the crystalpiece, and the crystal vibration element has a relation of 0<G/T≤0.5,where G is a distance between the long sides of the excitationelectrodes and the opposing long sides of the crystal piece, and T is athickness of the crystal piece between the excitation electrodes.

According to the present invention, a crystal vibration element and acrystal vibrator can be provided that can realize excellent vibrationcharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a crystal vibrator accordingto a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG. 1.

FIG. 3 is a perspective view of a crystal vibration element of thecrystal vibrator in FIG. 1.

FIG. 4A illustrates the vibration distribution of a thickness shearvibration of the crystal vibration element in FIG. 3.

FIG. 4B illustrates simulation results of the vibration distribution ofthe crystal vibration element in FIG. 3.

FIG. 4C illustrates simulation results of an X direction component ofthe vibration distribution (corresponding to X direction component ofcrystal orientation) of a crystal vibration element according to a firstmodification.

FIG. 4D illustrates simulation results of a Z direction component of thevibration distribution (corresponding to Y′ direction component ofcrystal orientation) of the crystal vibration element according to thefirst modification.

FIG. 4E illustrates simulation results of a Y direction component of thevibration distribution (corresponding to Z′ direction component ofcrystal orientation) of the crystal vibration element according to thefirst modification.

FIG. 5 is a side view of a crystal vibration element according to asecond modification.

FIG. 6 is a side view that illustrates a vibration state of a crystalvibration element according to an embodiment of the present invention inwhich the wavenumber n=4 in the case where the crystal vibration elementillustrated in FIG. 5 vibrates with a thickness shear vibration having amain vibration in a first direction.

FIG. 7 is a side view that illustrates a vibration state of a crystalvibration element according to an embodiment of the present invention inwhich the wavenumber n=5 in the case where the crystal vibration elementillustrated in FIG. 5 vibrates with a thickness shear vibration having amain vibration in a first direction.

FIG. 8 is a side view that illustrates a vibration state of a crystalvibration element according to a comparative mode to be compared withthe present invention in which the wavenumber n=4.5 in the case wherethe crystal vibration element illustrated in FIG. 5 vibrates with athickness shear vibration having a main vibration in a first direction.

FIG. 9A illustrates simulation results of an X direction component ofthe vibration distribution (corresponding to X direction component ofcrystal orientation) of a crystal vibration element according to a thirdmodification.

FIG. 9B illustrates simulation results of a Z direction component of thevibration distribution (corresponding to Y′ direction component ofcrystal orientation) of the crystal vibration element according to thethird modification.

FIG. 10 illustrates a crystal vibration element according to a fourthmodification.

FIG. 11A illustrates simulation results for a front-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification.

FIG. 11B illustrates simulation results for a rear-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification.

FIG. 11C illustrates simulation results of an X direction component at afront-surface side in the thickness direction of the vibrationdistribution (corresponding to X direction component of crystalorientation) of the crystal vibration element according to the fourthmodification.

FIG. 11D illustrates simulation results of an X direction component at arear-surface side in the thickness direction of the vibrationdistribution (corresponding to X direction component of crystalorientation) of the crystal vibration element according to the fourthmodification.

FIG. 11E illustrates simulation results of a Z direction component at afront-surface side in the thickness direction of the vibrationdistribution (corresponding to Y′ direction component of crystalorientation) of the crystal vibration element according to the fourthmodification.

FIG. 11F illustrates simulation results of a Z direction component at arear-surface side in the thickness direction of the vibrationdistribution (corresponding to Y′ direction component of crystalorientation) of the crystal vibration element according to the fourthmodification.

FIG. 11G illustrates simulation results of a Y direction component at afront-surface side in the thickness direction of the vibrationdistribution (corresponding to Z′ direction component of crystalorientation) of the crystal vibration element according to the fourthmodification.

FIG. 11H illustrates simulation results of a Y direction component at arear-surface side in the thickness direction of the vibrationdistribution (corresponding to Z′ direction component of crystalorientation) of the crystal vibration element according to the fourthmodification.

FIG. 11I illustrates simulation results of a front-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification in the case wherethe phase is 0°.

FIG. 11J illustrates simulation results of a front-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification in the case wherethe phase is substantially 45°.

FIG. 11K illustrates simulation results of a front-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification in the case wherethe phase is substantially 90°.

FIG. 11L illustrates simulation results of a front-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification in the case wherethe phase is substantially 135°.

FIG. 11M illustrates simulation results of a front-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification in the case wherethe phase is substantially 180°.

FIG. 11N illustrates simulation results of a front-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification in the case wherethe phase is substantially 225°.

FIG. 11O illustrates simulation results of a front-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the fourth modification in the case wherethe phase is substantially 270°.

FIG. 12A illustrates simulation results of a front-surface side in thethickness direction of the vibration distribution of a crystal vibrationelement according to a comparative example.

FIG. 12B illustrates simulation results of a rear-surface side in thethickness direction of the vibration distribution of the crystalvibration element according to the comparative example.

FIG. 12C illustrates simulation results of a Z direction component at afront-surface side in the thickness direction of the vibrationdistribution (corresponding to Y′ direction component of crystalorientation) of the crystal vibration element according to thecomparative example.

FIG. 12D illustrates simulation results of a Y direction component at afront-surface side in the thickness direction of the vibrationdistribution (corresponding to Z′ direction component of crystalorientation) of the crystal vibration element according to thecomparative example.

FIG. 13 illustrates a graph in which the vibration states in the firstmodification, the third modification, the fourth modification and thecomparative example are compared with each other.

FIG. 14 illustrates a crystal vibration element according to a fifthmodification of the present invention.

FIG. 15 is an exploded perspective view of a crystal vibrator accordingto a second embodiment of the present invention.

FIG. 16 is a sectional view taken along line XVI-XVI in FIG. 15.

FIG. 17 is an exploded perspective view of a crystal vibrator accordingto a third embodiment of the present invention.

FIG. 18 is a sectional view taken along line XVIII-XVIII in FIG. 17.

FIG. 19 is a perspective view of the crystal vibration elementillustrated in FIG. 14.

FIG. 20A is a graph for explaining the characteristics of a crystalvibration element according to the third embodiment of the presentinvention.

FIG. 20B is a graph for explaining the characteristics of the crystalvibration element according to the third embodiment of the presentinvention.

FIG. 21 is an equivalent circuit diagram of a crystal vibration element.

FIG. 22A is a graph for explaining the characteristics of the crystalvibration element according to the third embodiment of the presentinvention, and illustrates a case in which the width W of short sides ofthe crystal vibration element is small.

FIG. 22B is a graph for explaining the characteristics of the crystalvibration element according to the third embodiment of the presentinvention, and illustrates a case in which the width W of short sides ofthe crystal vibration element is large.

FIG. 23 is a graph for explaining the characteristics of the crystalvibration element according to the third embodiment of the presentinvention.

FIG. 24 is a perspective view of a crystal vibration element accordingto a first modification of the third embodiment of the presentinvention.

FIG. 25 is a perspective view of a crystal vibration element accordingto a second modification of the third embodiment of the presentinvention.

FIG. 26 is a perspective view of a crystal vibration element accordingto a third modification of the third embodiment of the presentinvention.

FIG. 27 is a perspective view of crystal vibration element of a crystalvibrator of the related art.

FIG. 28 illustrates the vibration distribution of a thickness shearvibration of the crystal vibration element of the related art in FIG.27.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, embodiments of the present invention will be described. Inthe following descriptions of the drawings, identical or similarconstituent elements will be denoted by identical or similar symbols.The drawings are exemplary, the dimensions and shapes of the individualparts are schematic, and the technical scope of the invention of thepresent application should not be interpreted as being limited to thatof the embodiments.

First Embodiment

A crystal vibrator 1 according to a first embodiment of the presentinvention will be described while referring to FIGS. 1 and 2. Here, FIG.1 is an exploded perspective view of the crystal vibrator, and FIG. 2 isa sectional view taken along line II-II in FIG. 1. In FIG. 2,illustration of various electrodes of a crystal vibration element 10 isomitted.

As illustrated in FIG. 1, the crystal vibrator 1 according to thisembodiment includes the crystal vibration element 10, a cap 20, which isan example of a lid member, and a substrate 30, which is an example of asupport body that supports the crystal vibration element 10. The cap 20and the substrate 30 form a holder (case or package) that is foraccommodating the crystal vibration element 10.

The crystal vibration element 10 includes a crystal piece 11, andexcitation electrodes 14 a and 14 b (hereafter, also referred to as“first excitation electrode 14 a and second excitation electrode 14 b”)that are respectively provided on a front surface and a rear surface ofthe crystal piece 11. The first excitation electrode 14 a is provided ona first surface 12 a (front surface), which is a main surface, of thecrystal piece 11, and the second excitation electrode 14 b is providedon a second surface 12 b (rear surface), which is a main surface, of thecrystal piece 11 that opposes the first surface 12 a of the crystalpiece 11.

The crystal piece 11 has a trigonal-system crystal structure, which isdifferent from the cubic system of a piezoelectric ceramic, for example,and is formed of a crystal material having a prescribed crystalorientation. The crystal vibration element 10 includes an AT-cut crystalpiece 11, for example. The AT-cut crystal piece 11 is obtained bycutting a crystal such that surfaces parallel to a plane specified by anX axis and a Z′ axis (hereafter “XZ′ plane,” and which similarly appliesto planes specified using other axes) become main surfaces of thecrystal in the case where a Y′ axis and a Z′ axis are axes that areobtained by respectively rotating a Y axis and a Z axis, among an Xaxis, a Y axis and a Z axis that are crystal axes of an artificialcrystal, around the X axis by 35° 15′±1′30″ in a direction from the Yaxis toward the Z axis. In the example illustrated in FIG. 1, thecrystal piece 11, which is an AT-cut crystal piece, has long sides thatare parallel to the X axis serving as a first direction, and short sidesthat are parallel to the Z′ axis serving as a second direction that isorthogonal to the first direction. In addition, the crystal piece 11 hasa thickness that is parallel to the Y′ axis serving as a third directionthat is orthogonal to the first direction and the second direction.Hereafter, a direction along the long sides, a direction along the shortsides and the thickness may be respectively referred to as alongitudinal direction, a lateral direction and a thickness direction.The crystal piece 11 is formed in a rectangular shape when the XZ′ planeis viewed in plan. A crystal vibration element that uses an AT-cutcrystal piece has a property of having very high frequency stabilityover a wide range of temperatures, and is also excellent in terms ofdeterioration over time. Furthermore, a main vibration of an AT-cutcrystal vibration element is a thickness shear mode vibration.Hereafter, the individual constituent elements of the crystal vibrator 1will be described while referring to the AT-cut axis directions.

The crystal piece 11 according to this embodiment is not limited to theabove-described configuration, and for example an AT-cut crystal piecehaving long sides that are parallel to the Z′ axis and short sides thatare parallel to the X axis may be used instead. Alternatively, so longas the main vibration is the thickness shear mode, the crystal piece 11may be a crystal piece having a different kind of cut than an AT cutsuch as a BT cut, for example. However, an AT-cut crystal piece, whichhas very high frequency stability over a wide range of temperatures, ismost preferable.

The first excitation electrode 14 a is formed on the first surface 12 aof the crystal piece 11, and the second excitation electrode 14 b isformed on the second surface 12 b of the crystal piece 11. The first andsecond excitation electrodes 14 a and 14 b are arranged as a pair ofelectrodes having the crystal piece 11 interposed therebetween so as tobe substantially entirely superposed with each other when the XZ′ planeis viewed in plan. The first and second excitation electrodes 14 a and14 b each have a rectangular shape when the XZ′ surface is viewed inplan. For example, as illustrated in FIG. 1, the excitation electrodesare provided such that the long sides of the excitation electrodes areparallel to the short sides of the crystal piece 11, and the short sidesof the excitation electrodes are parallel to the long sides of thecrystal piece 11.

The crystal vibration element is not limited to this configuration, andcan instead be implemented as a crystal element vibration element havinga long thin plate shape in the X direction of the crystal orientation asillustrated in FIGS. 4C to 4E as a first modification that is describedlater. In other words, the excitation electrodes may also be providedsuch that the long sides of the excitation electrodes are parallel tothe long sides of the crystal piece 11, and the short sides of theexcitation electrodes are parallel to the short sides of the crystalpiece 11.

A connection electrode 16 a that is electrically connected to the firstexcitation electrode 14 a via an extension electrode 15 a and aconnection electrode 16 b that is electrically connected to the secondexcitation electrode 14 b via an extension electrode 15 b are formed onthe crystal piece 11. Specifically, the extension electrode 15 a extendsfrom the first excitation electrode 14 a toward the short side of thecrystal piece 11 on the negative X axis direction side on the firstsurface 12 a, passes over a side surface of the crystal piece 11 on thenegative Z′ axis direction side and is connected to the connectionelectrode 16 a formed on the second surface 12 b. On the other hand, theextension electrode 15 b extends from the second excitation electrode 14b toward the short side of the crystal piece on the negative X axisdirection side on the second surface 12 b, and is connected to theconnection electrode 16 b formed on the second surface 12 b. Theconnection electrodes 16 a and 16 b are arranged along the short side ofthe crystal piece 11 on the negative X axis direction side, and theconnection electrodes 16 a and 16 b are electrically connected to andmechanically held by the substrate 30 via conductive holding members 36a and 36 b, which are formed by applying and curing a conductiveadhesive. The connection electrodes 16 a and 16 b and the extensionelectrodes 15 a and 15 b are not limited to these arrangements andpattern shapes, and can be changed as appropriate by considering theelectrical connections between these electrodes and other members. Anelectrode superposition region in which the first excitation electrode14 a and the second excitation electrode 14 b are superposed with eachother in plan view is provided so as to be a prescribed distance fromthe short sides of the crystal piece 11. The distance from the shortsides of the crystal piece 11 to the electrode superposition region islarger than a distance from the long sides of the crystal piece 11 tothe electrode superposition region.

The first and second excitation electrodes 14 a and 14 b, the extensionelectrodes 15 a and 15 b, and the connection electrodes 16 a and 16 bare formed by forming a chromium (Cr) layer, which is for increasing theadhesive force to the front surface of the crystal piece 11, and forminga gold (Au) layer on the underlying surface of the chromium layer. Theelectrodes are not limited to these materials.

As illustrated in FIG. 2, the cap 20 has a recess 24 that opens toward afirst surface 32 a of the substrate 30. The recess 24 is provided with aside wall portion 22 that is formed so as to stand upright from a bottomsurface of the recess 24 along the entire periphery of the opening ofthe recess 24. In addition, the cap 20 also has a flange portion 28 thatprotrudes from the side wall portion 22 in a direction away from theopening. In this case, the flange portion 28 has a facing surface 26that faces the first surface 32 a of the substrate 30. The width of thefacing surface 26 is larger than the thickness of the side wall portion22 of the cap 20. Thus, since the area of the bond between the cap 20and the substrate 30 can be increased by bonding the flange portion 28and the substrate 30 to each other, it is possible to improve thestrength of the bond between the cap 20 and the substrate 30.

The shape of the cap 20 is not particularly limited in this embodiment,and for example, a leading end of the side wall portion 22 formed so asto stand upright at substantially right angles to the bottom surface ofthe recess 24 may be bonded to the substrate 30 without the cap 20having the flange portion 28.

The material of the cap 20 is not particularly limited, and the cap 20may be formed of a conductive material such as a metal. In this way, ashielding function can be added by electrically connecting the cap 20 tothe ground potential. Alternatively, the cap 20 may be formed of aninsulating material or may have a composite structure constituted by aconductive material and an insulating material.

The substrate 30 supports the crystal vibration element 10 in such amanner that the crystal vibration element 10 can be excited. In theexample illustrated in FIG. 1, the crystal vibration element 10 issupported so as to be able to be excited on the first surface 32 a ofthe substrate 30 via the conductive holding members 36 a and 36 b.

In the example illustrated in FIG. 1, the substrate 30 has long sidesthat are parallel to the X axis direction, short sides that are parallelto the Z′ axis direction, and a thickness that is parallel to the Y′axis direction, and has a rectangular shape in the XZ′ plane. Thesubstrate 30 may be formed of an insulating ceramic for example, and maybe formed by stacking a plurality of insulating ceramic sheets on top ofone another and then firing the insulating ceramic sheets.Alternatively, the substrate 30 may be formed of a glass material (forexample, a material having silicate glass as a main component or amaterial having a main component other than silicate, and exhibiting aglass transition phenomenon with an increase in temperature), a crystalmaterial (for example, AT cut crystal), or a glass epoxy resin, forexample. The substrate 30 is preferably formed a heat-resistantmaterial. The substrate 30 may be formed of a single layer or aplurality of layers, and in the case where the substrate 30 is formed ofa plurality of layers, an insulating layer may be formed as theuppermost layer that forms the first surface 32 a. Furthermore, thesubstrate 30 may have a flat plate-like shape, or may have a concaveshape that opens in a direction so as to face the cap 20. As illustratedin FIG. 2, the cap 20 and the substrate 30 are bonded to each other viaa bonding material 70, and as a result, the crystal vibration element 10is hermetically sealed in an internal space (cavity) 23 enclosed by therecess 24 of the cap 20 and the substrate 30. In this case, it ispreferable that the pressure of the internal space be that of a vacuumstate having a pressure lower than atmospheric pressure in order to makeit possible to reduce deterioration of the first and second excitationelectrodes 14 a and 14 b that occurs over time due to oxidation.

The bonding material 70 is provided along the entire peripheries of thecap 20 and the substrate 30, and is interposed between the facingsurface 26 of the side wall portion 22 of the cap 20 and the firstsurface 32 a of the substrate 30. The bonding material 70 is composed ofan insulating material. As the insulating material, a glass adhesivematerial such as a low-melting-point glass (for example, a lead boricacid based or tin phosphoric acid based glass), or a resin adhesive maybe used. With these insulating materials, the cost is low compared withmetal bonding, and a heating temperature can be suppressed and themanufacturing process can be simplified. If metal bonding is used, ahigher bonding strength can be obtained compared with bonding using aresin adhesive.

In the example illustrated in FIG. 2, one end of the crystal vibrationelement 10 is fixed in place by the conductive holding members 36 a and36 b, and the other end of the crystal vibration element 10 is free. Inaddition, both ends of the crystal vibration element 10 in the directionof the long sides or the short sides may be fixed to the substrate 30,as a modification.

As illustrated in FIG. 1, the substrate 30 includes connectionelectrodes 33 a and 33 b that are formed on the first surface 32 a, andextension electrodes 34 a and 34 b that extend from the connectionelectrodes 33 a and 33 b to the outer edge of the first surface 32 a.

The connection electrode 16 a of the crystal vibration element 10 isconnected to the connection electrode 33 a via the conductive holdingmember 36 a, and the connection electrode 16 b of the crystal vibrationelement 10 is connected to the connection electrode 33 b via theconductive holding member 36 b.

The extension electrode 34 a extends from the connection electrode 33 ato any corner of the substrate 30, and the extension electrode 34 bextends from the connection electrode 33 b to another corner of thesubstrate 30. In addition, a plurality of outer electrodes 35 a, 35 b,35 c and 35 d are formed at the corners of the substrate 30. In theexample illustrated in FIG. 1, the extension electrode 34 a is connectedto the outer electrode 35 a formed at the corner on the positive Z′ axisdirection and negative X axis direction side, and the extensionelectrode 34 b is connected to the outer electrode 35 b formed at thecorner on the negative Z′ axis direction and positive X axis directionside. In addition, as illustrated in FIG. 1, the outer electrodes 35 cand 35 d may be formed at the remaining corners, and these outerelectrodes may be dummy electrodes that are not electrically connectedto the crystal vibration element 10. In other words, the dummyelectrodes need not be electrically connected to the first and secondexcitation electrodes 14 a and 14 b. In addition, the dummy electrodesmay be connected to terminals (terminals that are not connected toanother electronic element) provided on a mounting substrate (notillustrated) on which the crystal vibrator 1 is mounted. By forming suchdummy electrodes, adding the conductive material for forming the outerelectrodes becomes easier, and since the outer electrodes can be formedat all the corners, a processing step of electrically connecting thecrystal vibrator to other members is simplified. In addition, ratherthan being dummy electrodes, the outer electrodes 35 c and 35 d mayinstead serve as ground electrodes to which a ground potential issupplied. In the case where the cap 20 is composed of a conductivematerial, the cap 20 can be given a shielding function by connecting thecap 20 to the outer electrodes 35 c and 35 d serving as groundelectrodes.

In the example illustrated in FIG. 1, the corners of the substrate 30each have a notched side surface that is formed by cutting away part ofthe corner to form a cylindrical curved surface shape (also referred toas a castellation shape), and the outer electrodes 35 a to 35 d are eachformed so as to extend across the first surface 32 a, the notched sidesurface and a second surface 32 b of the substrate 30 in a continuousmanner. The shape of the corners of the substrate 30 is not limited tothis shape, and the notched shape may instead be a planar shape, or thefour corners may each have a right-angle rectangular shape in plan viewwithout having a notch.

The configurations of the connection electrodes 33 a and 33 b, theextension electrodes 34 a and 34 b and the outer electrodes 35 a to 35 dof the substrate 30 are not limited to the configurations describedabove, and may be modified and used in various ways. For example, theconnection electrodes 33 a and 33 b may be arranged on different sidesof the first surface 32 a of the substrate 30 such as one being formedon the positive X axis direction side and the other being formed on thenegative X axis direction side. In this configuration, the crystalvibration element 10 would be supported by the substrate 30 at both oneend and the other end thereof in the long side direction. Furthermore,the number of outer electrodes is not limited to being four, and forexample, there may be two outer electrodes arranged at opposite corners.In addition, the outer electrodes are not limited to being arranged atthe corners, and may be formed on parts of the side surfaces of thesubstrate 30 excluding the corners. In this case, as already describedabove, notched side surfaces may be formed by cutting away parts of sidesurfaces to form cylindrical curved surfaces, and outer electrodes maybe formed on those parts of the side surfaces excluding the corners. Inaddition, the other outer electrodes 35 c and 35 d that serve as dummyelectrodes need not be formed. Furthermore, through holes that penetratefrom the first surface 32 a to the second surface 32 b may be formed inthe substrate 30, and electrical connections from connection electrodesformed on the first surface 32 a to the second surface 32 b may berealized by via conductors provided inside the through holes.

In the crystal vibrator 1 illustrated in FIG. 1, an alternating electricfield is applied between the pair of first and second excitationelectrodes 14 a and 14 b of the crystal vibration element 10 via theouter electrodes 35 a and 35 b of the substrate 30. Thus, the crystalpiece 11 vibrates with a thickness shear vibration being a mainvibration mode, and resonance characteristics are obtained along withthis vibration.

Next, the crystal vibration element will be described in more detailwhile referring to FIGS. 3 to 14. FIG. 3 is a perspective view of thecrystal vibration element 10, and FIGS. 4A and 4B illustrates avibration distribution of the thickness shear vibration of the crystalvibration element 10. More specifically, FIG. 4A is a schematic diagramand FIG. 4B illustrates simulation results. Here, for convenience ofexplanation, only the vibration distribution corresponding to the firstexcitation electrode 14 a and the second excitation electrode 14 b isillustrated in FIGS. 4A and 4B. In addition, FIGS. 4C to 14 are fordescribing crystal vibration elements according to modifications of thisembodiment and a comparative example.

FIG. 3 illustrates an example of the crystal piece 11, the firstexcitation electrode 14 a and the second excitation electrode 14 b ofthe crystal vibration element 10 according to this embodiment. In thisexample, when the XZ′ plane is viewed in plan, the short side of theexcitation electrode 14 a on the positive Z′ axis direction side issuperposed with the long side of the crystal piece 11 on the positive Z′axis direction side, and the short side of the excitation electrode 14 aon the negative Z′ axis direction side is superposed with the long sideof the crystal piece 11 on the negative Z′ axis direction side. Inaddition, similarly for the excitation electrode 14 b, when the XZ′plane is viewed in plan, the short side of the excitation electrode 14 bon the positive Z′ axis direction side is superposed with the long sideof the crystal piece 11 on the positive Z′ axis direction side, and theshort side of the excitation electrode 14 b on the negative Z′ axisdirection side is superposed with the long side of the crystal piece 11on the negative Z′ axis direction side. In other words, the excitationelectrode 14 a is provided on the first surface 12 a of the crystalpiece 11 so as to extend to both sides of the main surface the crystalpiece 11 in the Z′ axis direction, and the excitation electrode 14 b isprovided on the second surface 12 b of the crystal piece 11 so as toextend to both sides of the main surface of the crystal piece 11 in theZ′ axis direction.

In addition, the crystal vibration element 10 is configured to havedimensions of L=1.322 mm, W=0.895 mm, T=0.0426 mm, EL=0.640 mm and G=0,for example, where L is the length of the long sides of the crystalpiece 11, W is the length of the short sides of the crystal piece 11, Tis the thickness of the crystal piece 11 in the Y′ axis direction, andEL is the length of the short sides of the excitation electrode 14 a inthe X axis direction. G/T=0, W/T=21.0 and L/T=31.0. Here, G is thedistance between the short sides of the excitation electrodes and thelong sides of the crystal piece, and since the short sides of theexcitation electrodes and the long sides of the crystal piece arealigned with each other in FIG. 3, G=0. The above-listed dimensions aremerely examples, and the crystal vibration element according to thisembodiment includes configurations having the vibration distributionsdescribed below (includes shapes and dimensions of the crystal piece andthe excitation electrodes and the positional relationshipstherebetween).

FIG. 4B illustrates the results of a simulation of a thickness shearvibration generated in the crystal vibration element 10 in FIG. 3 whenan alternating electric field of a prescribed oscillation frequency, forexample, the AT-cut fundamental oscillation frequency, is applied, thesimulation being performed using a software package called Femtet(registered trademark) manufactured by Murata Manufacturing Co., Ltd.and using a piezoelectric analysis solver under the condition of a meshsize of 0.02 mm. FIG. 4A is a schematic diagram of the same. Thematerial constants are quoted from Kagaku Binran Kisohen II Revised 4thEdition, The Chemical Society of Japan, Maruzen (1993); ChronologicalScientific Tables 1996, National Astronomical Observatory of Japan,Maruzen (1996); Danseihasoshigijutsu Handbook, Japan Society for thePromotion of Science Danseihasoshigijutsu 150th Committee, Ohmsha; andHyomendanseihasoshizairyo Databook, Japan Electronics and InformationTechnology Industries Association. The above description also similarlyapplies to the drawings illustrating other simulation results.

As illustrated in FIG. 4B, an X direction among vibration directions ofthe vibration distribution corresponds to an X direction of the crystalorientation, a Y direction among the vibration directions of thevibration distribution corresponds to a Z′ direction of the crystalorientation, and a Z direction among the vibration directions of thevibration distribution corresponds to a Y′ direction of the crystalorientation. The same relationships between the vibration directions andthe crystal orientation similarly apply to the drawings illustratingother simulation results. Hereafter, description will be given on thebasis of the crystal orientation directions unless stated otherwise.

As illustrated in FIGS. 4A and 4B, a vibration distribution, in whichthe main vibration is a thickness shear vibration in which the crystalvibration element 10 mainly vibrates in the X direction, includes avibration region 40 that extends in a band-like shape in the Z′ axisdirection (lateral direction) of the crystal piece 11 and non-vibrationregions 50 a and 50 b that are adjacent to the two sides of thevibration region 40 in the X axis direction (longitudinal direction) ofthe crystal piece 11. In other words, the non-vibration regions 50 a and50 b are not adjacent to each other. Here, in the present invention, theterm “vibration region” refers to a region in which the largestdisplacement is generated in the crystal piece by the main vibration,which is thickness shear vibration, when an alternating electric fieldof a prescribed oscillation frequency (for example, the AT-cutfundamental oscillation frequency) is applied. In addition, in thepresent invention, the term “non-vibration region” refers to a region inwhich the largest displacement is not generated in the crystal piecewhen the vibration region of the crystal piece vibrates due to the mainvibration, and this term is not limited to a region where there isabsolutely no displacement due to vibration and may be a region wherethe displacement due to vibration is smaller than in the vibrationregion. It is preferable that a non-vibration region be a region inwhich the amount of displacement is less than 20-25% the maximum amountof displacement. In addition, when the XZ′ plane is viewed in plan, thevibration region 40 has a band-like shape that extends in a continuousmanner from one long side of the crystal piece 11 that is parallel tothe X axis to the other side of the crystal piece 11 that is similarlyparallel to the X axis. The vibration region 40 does not reach either ofthe two short sides of the crystal piece 11 that are parallel to the Z′axis. When the XZ′ plane is viewed in plan, the boundaries where thevibration region 40 and the non-vibration regions 50 a and 50 b areadjacent to each other are not straight lines, but rather have awave-like shape made up of alternating peaks and troughs. Thesewave-shaped boundaries have a substantially sinusoidal shape in whichthe heights of the peaks and the depths of the troughs are substantiallythe same as each other and that has a substantially constant period. Atthis time, it is preferable that the difference between the height ofpeak and the depth of a trough be within ±25% using a central portionbetween a peak and a trough as a reference. Regarding the phrase “thevibration region 40 extends in a band-like shape”, it is sufficient thatthe vibration region 40 have a certain width and extend in a certaindirection and the vibration region 40 is not limited to having a longthin shape in the extension direction. For example, the phrase may alsorefer to a configuration in which the length of the vibration region 40in the extension direction is smaller than the width of the vibrationregion 40.

Here, when the XZ′ plane is viewed in plan, the region occupied by thevibration region 40 may substantially coincide with the region occupiedby the excitation electrodes 14 a and 14 b in FIG. 3. In this case, thevibration region 40 has a band-like shape that continuously extends fromone short side of each of the excitation electrodes 14 a and 14 b thatis parallel to the X axis to the other short side of each of theexcitation electrodes 14 a and 14 b that is similarly parallel to the Xaxis. Furthermore, although the boundaries where the vibration region 40and the non-vibration regions 50 a and 50 b are adjacent to each otherhave a wave-like shape as described above, the boundaries are roughlyaligned with the long sides of the excitation electrodes 14 a and 14 bthat are parallel to the Z′ axis.

FIG. 4A illustrates the displacement distribution for the instant whenthe vibration of the main surfaces exhibits the maximum displacement inthe configuration in FIG. 3. The displacement distribution is equallydivided into four types of regions on the basis of the value of themaximum displacement of the vibration region 40, namely, three vibrationregions and one non-vibration region, and the vibration region isillustrated using different types of hatching. That is, the vibrationregion 40 includes a first vibration strength region 42, secondvibration strength regions 44 a and 44 b in which the amount ofdisplacement due to the vibration is smaller than in the first vibrationstrength region 42, and third vibration strength regions 46 a and 46 bin which the amount of displacement due to the vibration is smaller thanin the second vibration strength regions 44 a and 44 b. When the XZ′plane is viewed in plan, the second vibration strength regions 44 a and44 b are adjacent to the two sides of the first vibration strengthregion 42 in the X axis direction (longitudinal direction) of thecrystal piece 11. Furthermore, the third vibration strength regions 46 aand 46 b are respectively adjacent to the sides of the second vibrationstrength regions 44 a and 44 b that are not adjacent to the firstvibration strength region 42 in the X axis direction (longitudinaldirection) of the crystal piece 11. In other words, when a center linethat is parallel to the Z′ axis is drawn in the center of the firstvibration strength region 42, the vibration region 40 has a vibrationdistribution that is symmetrical about the center line. Thenon-vibration regions 50, in which the amount of displacement is 0-25%the maximum amount of displacement, that is, 0-85 nm, illustrated inFIG. 4A, are adjacent to the sides of the third vibration strengthregions 46 a and 46 b that are not adjacent to the second vibrationstrength regions 44 a and 44 b in the X axis direction (longitudinaldirection) of the crystal piece 11. In the example illustrated in FIG.4, the amount of displacement of the first vibration strength region 42is 75-100% the maximum amount of displacement, that is, around 255-340nm, the amount of displacement of the second vibration strength regions44 a and 44 b is around 50-75% the maximum amount of displacement, thatis, 170-255 nm, and the amount of displacement of the third vibrationstrength regions 46 a and 46 b is 25-50% the maximum amount ofdisplacement, that is, 85-170 nm. When the XZ′ plane is viewed in plan,each of these vibration strength regions has a band-like shape thatextends in a continuous manner from one long side of the crystal piece11 that is parallel to the X axis to the other long side of the crystalpiece 11 that is similarly parallel to the X axis. The vibrationstrength regions do not reach either of the two short sides of thecrystal piece 11 that are parallel to the Z′ axis. In addition, theboundaries where these vibration strength regions are adjacent to eachother are not straight lines, but rather meander in a wave-like shape.The wave-shaped boundaries have a substantially sinusoidal shape, forexample.

In addition, the vibration region 40 has a strong vibration region(includes apex of vibration) that represents an amount of displacementof 90% or more of the maximum amount of displacement. For example, asillustrated in FIGS. 4A and 4B, the first vibration strength region 42of the vibration region 40 includes a strong vibration region. Asillustrated in FIG. 4B, the strong vibration region has firstdistributions having opposite phases from each other that are located atone long side of the front surface (first main surface 12 a) of thecrystal piece 11 that extends along the X axis direction, and anotherlong side of the rear surface (second main surface 12 b) of the crystalpiece 11 that extends along the X axis direction and is separated fromand faces the one long side in the Z′ axis direction. The firstdistributions are semi-elliptical distributions having a shape obtainedby vertically halving an ellipse having a long axis that extends in theX axis direction (longitudinal direction) of the crystal piece 11. Inaddition, the strong vibration region has second distributions that arearranged next to each other in the Z′ axis direction and are located atthe front surface (first main surface 12 a) and the rear surface (secondmain surface 12 b) of the crystal piece 11. The second distributions aresubstantially elliptical distributions having a long axis that extendsin the X axis direction of the crystal piece 11 as illustrated in FIG.4B. Thus, the first vibration strength region 42 in FIG. 4A has aplurality of strong vibration regions in the Z′ axis direction (lateraldirection). In FIG. 4A, the outer edge of the first vibration strengthregion 42, which includes a plurality of strong vibration regions, isillustrated.

In addition, as illustrated in FIG. 4D, the strong vibration region of adisplacement component in the Z axis direction (Y′ axis direction ofcrystal orientation) based on the simulation model has a thirddistribution in which one half thereof and the other half thereof in theX axis direction of the crystal orientation have opposite phases. Morespecifically, with reference to a center line that extends in the Z′axis direction of the crystal orientation at a center point in the Xaxis direction of the crystal orientation of the crystal piece, thisstrong vibration region further has a third distribution that includes aplurality of one distributions that are on one side of the center linein the X axis direction and are arrayed in the X axis direction, and aplurality of other distributions that are on the other side of thecenter line in the X axis direction, are arrayed in the X axisdirection, and have the opposite phase to the one distributions.

Here, in this embodiment, in the crystal piece obtained by AT cutting acrystal material that is a trigonal piezoelectric crystal having aprescribed crystal orientation, a novel thickness shear mode isgenerated in which a thickness shear mode is a main vibration mode andthat is distributed in a band-like shape in the second direction whereboundaries with non-vibration regions have a wave-like shape, asobtained in the present invention as illustrated in FIGS. 4A and 4B, andthe thickness shear mode has a strong vibration region (includes avibration apex or antinode) in which the vibration has opposite phasesat diagonally opposite sides of the front and rear surfaces. Hereafter,such a thickness shear mode included in the present invention isreferred to as a full-width thickness shear mode. In the full-widththickness shear mode, the strong vibration region, in which thevibration has opposite phases at diagonally opposite sides of the frontand rear surface, preferably has a semi-elliptical distribution having ashape obtained by vertically halving an ellipse that is elongated in theX direction (refer to FIGS. 4A to 4E).

Next, the embodiment will be compared and contrasted with an example ofthe related art while referring to FIGS. 27 and 28. FIG. 27 illustratesa crystal vibration element of the related art in which a thicknessshear vibration is confined to a central portion of a crystal piece.This example of the related art differs from the configuration in FIG.4A in that a length EW of an excitation electrode in the lateraldirection is 0.554 mm, in that the length EW is set so as to be smallerthan in FIG. 4A, and in that a gap of G/T=4 is provided from an endsurface of the crystal piece. In other words, the crystal vibrationelement illustrated in FIG. 27 includes an excitation electrodenon-formation region that is provided in an annular shape around anouter periphery of the crystal piece, and an excitation electrodeformation region that is provided in a central portion of the crystalpiece inside the excitation electrode non-formation region that isprovided in an annular shape. FIG. 28 schematically illustrates thevibration distribution of the thickness shear mode of the crystalvibration element of the related art illustrated in FIG. 27. FIG. 28illustrates a vibration distribution having an amplitude antinode in thecentral portion of the crystal piece, and an amplitude node that extendsin a continuous manner around the entire periphery of the amplitudeantinode. In addition, when the front surface of the crystal piece isviewed in plan, amplitude antinodes that exist on the front and rearsurfaces are at overlapping positions. As illustrated in FIG. 28, whenthe XZ′ plane is viewed in plan, the crystal vibration element of theexample of the related art includes, in the form of substantiallyconcentric circles arrayed from a central portion of the crystal piecetoward the outside of the crystal piece, a first vibration strengthregion in which the displacement due to the vibration is largest, asecond vibration strength region that is located in a region surroundingthe first vibration strength region and in which the displacement due tothe vibration is smaller than in the first vibration strength region,and a third vibration strength region that is located in the regionsurrounding the second vibration strength region and in which thedisplacement due to the vibration is smaller than in the secondvibration strength region.

In contrast, a thickness shear amplitude node or a non-vibration regionthat surrounds the central portion of the crystal piece in an annularmanner such as in the thickness shear mode of the related artillustrated in FIG. 27 does not exist in the full-width thickness shearmode according to this embodiment. Furthermore, as illustrated in FIG.4A, at least one amplitude antinode exists inside a vibration regionthat is distributed in a band-like shape laterally extending between thetwo opposite ends of the crystal piece in the second direction. Inaddition, when the front surface of the crystal piece is viewed in plan,amplitude antinodes that exist on the front and rear surfaces are atnon-overlapping positions. Consequently, in contrast to the thicknessshear mode in which there is one antinode at overlapping positions onthe front and rear surfaces of the central portion of the crystal piecein the example of the related art illustrated in FIG. 28, thisembodiment has the vibration distribution illustrated in FIG. 4A andtherefore a larger vibration region can be secured along the Z′ axisdirection of the crystal piece. In addition, in a thickness shearvibration that depends on a thickness T of a crystal piece sandwichedbetween excitation electrodes, by making the length L of the crystalpiece in the X axis direction larger than the length EL of theexcitation electrodes in the X axis direction by a prescribed ratio, notonly can a full-width thickness shear mode that exists in the firstdirection illustrated in FIG. 4A be excited, but also a full-widththickness shear mode that includes a vibration state in which vibrationsof a plurality of wavenumbers in which the crystal piece is displaced inthe third direction inside the vibration region are distributed in thefirst direction. Furthermore, provided that the ratio of the length L ofthe crystal piece in the first direction with respect to the length ELis set to fall within a prescribed range, amplitude nodes of thefull-width thickness shear mode that extend in a continuous manner inthe Z′ axis direction can be arranged at the ends of the crystal piecein the first direction. Therefore, provided that the crystal piece issupported by holding members at the positions of the amplitude nodes ofthe full-width thickness shear mode, the effect of such support on thefull width shear mode such as leakage or obstruction of the vibrationcan be made small.

As described above, in this embodiment, a specific vibration that iscalled a full-width thickness shear vibration in the present inventioncan be selectively generated in the vibration distribution of athickness shear vibration so as to extend across the Z′ axis direction(lateral direction) of the crystal vibration element 10, and therefore auniform vibration can be obtained. Therefore, a DLD characteristic canbe improved, and since a CI value can be made low and the value of acapacitance ratio γ can be made small by securing a wide vibrationregion 40, excellent vibration characteristics can be obtained.

Next, a first modification will be described while referring to FIGS. 4Cto 4E. In the following description, points that are different from theabove-described content will be described. In this modification, thecrystal vibration element has the same configuration as in FIG. 3 inthat the crystal vibration element has a long thin plate shape in the Xdirection, but differs from the configuration in FIG. 3 in that thelongitudinal direction of excitation electrodes matches the longitudinaldirection of the crystal piece 11, and in that the lateral direction ofthe excitation electrodes matches the lateral direction of the crystalpiece 11. Specifically, in this modification, W=0.277 mm, T=0.033 mm,L=0.77 mm, EL=0.44 mm and Tex=0.267 μm, and G/T=0, W/T=8.39, L/T=23.7and EL/T=12.8. FIG. 4C illustrates the displacement distribution of an Xdirection component of a vibration distribution (corresponding to an Xdirection component of the crystal orientation) obtained by asimulation, FIG. 4D illustrates the displacement distribution of a Zdirection component of the vibration distribution (corresponding to a Y′direction component of the crystal orientation) obtained by asimulation, and FIG. 4E illustrates the displacement distribution of a Ydirection component of the vibration distribution (corresponding to a Z′direction component of the crystal orientation) obtained by asimulation. It is clear from FIG. 4C that the displacement distributionof the X direction component, which represents the main vibration of thevibration, shows the displacement distribution of a full-width thicknessshear vibration that has a vibration region that is sandwiched betweennon-vibration regions located at both ends of the crystal vibrationelement in the X direction and that connects the opposite long sides toeach other. In addition, when the displacement is divided into tengradations of displacement between the largest positive value and thesmallest negative value, in the distribution state of a strong vibrationregion on the negative displacement side representing at least 80% ofthe largest absolute value of negative displacement, which representsthe maximum displacement, two elliptical distributions that extend inthe X direction and a semi-elliptical distribution having a shapeobtained by vertically halving an ellipse are arrayed in the widthdirection. The semi-elliptical distribution is distributed so as toextend along a long side with the center thereof located on the longside. At this time, the largest value of the displacement of the Xdirection component is 5.668 μm, the largest value of the Z (thickness)direction component of the vibration distribution is 0.603 μm, and thelargest value of the displacement of the Y direction (width) componentof the vibration distribution is 0.966 μm.

Next, a second modification will be described while referring to FIGS. 5to 8,

A crystal vibration element 210 includes a mesa-shaped crystal piecehaving a first part 240 and second parts 250. The first part 240 has avibration region that extends in a band-like shape in the Z′ axisdirection similarly to the vibration regions described in FIGS. 3 to 4B.When the XZ′ plane is viewed in plan, the second parts 250 are providedat a position that contacts one side, which is parallel to the Z′ axis,of the first part 240, which is the vibration region, and at a positionthat contacts the other side, which is similarly parallel to the Z′axis, of the first part 240. A side view of the crystal vibrationelement 210 in which the crystal vibration element is viewed from theXY′ plane includes the crystal piece first part 240 that is sandwichedbetween a first excitation electrode 214 a, which has a thickness Tex1,and a second excitation electrode 214 b, which has a thickness Tex2. Thefirst part 240 has a vibration region having a thickness T when the XY′plane is viewed in plan. In addition, a thickness Tpe of the secondparts 250 is smaller than a thickness T of the first part 240. Asillustrated in FIG. 5, the pair of excitation electrodes 214 a and 214 bare provided so as to have the length EL in the X axis direction so asto entirely cover the X axis direction length L1 of the vibration regionof the first part 240 that is located in the center of the crystal piecein the X axis direction, and therefore L1=EL.

FIG. 6 illustrates the displacement distribution of vibration for thecrystal vibration element 210 illustrated in FIG. 5, in which athickness shear vibration is the main vibration, in the case where avibration mode having a wavenumber n=4 is excited in a vibration regionthat satisfies the following formulas 1 and 2 and has an X axisdirection length L1.

T is the thickness of the crystal piece in the vibration region, L1 isthe length of the first part in the X axis direction, Tex is the totalthickness of the thickness Tex1 of the first excitation electrode andthe thickness Tex2 of the second excitation electrode, γex is thespecific gravity of the material of the excitation electrodes, and γxtis the specific gravity of the material of the crystal piece. Formula 1below gives the effective thickness Te of the vibration region of thecrystal vibration element, which is calculated by adding to the value ofthe thickness T of the crystal piece, a value obtained by multiplying aratio of the specific gravity γex of the material of the excitationelectrodes to the specific gravity γxt of the material of the crystalpiece by the thickness Tex of the excitation electrodes. n (n is anatural number) is the wavenumber in the vibration region in the X axisdirection. In the following formulas 1 and 2, it is assumed that theexcitation electrode 214 a and the excitation electrode 214 b areprovided so as to be formed of the same material and have the samethickness.Te=T+Tex·γex/γxt  Formula 1L1/Te=1.603·n−0.292  Formula 2

From the vibrational displacement distribution in FIG. 6, it is clearthat, in the crystal vibration element 210, vibrational displacement isconfined to inside the vibration region of the first part 240 and thatthe vibrational displacements of the second parts 250 are sufficientlysmall compared with that of the first part 240.

FIG. 7 illustrates the displacement distribution of vibration in acrystal vibration element 212 that is formed so as to satisfy formulas 1and 2 when n=5. From the vibrational displacement distribution in FIG.7, it is clear that vibrational displacement is confined to inside thevibration region of a first part 241 and that the vibrationaldisplacements of second parts 251 are sufficiently small compared withthat of the first part 241 also in the case where n=5.

As a comparative example, FIG. 8 illustrates the displacementdistribution of vibration in a crystal vibration element 214 that isformed so as to satisfy formulas 1 and 2 when n=4.5 (in other words,when n is not a natural number). From the vibrational displacementdistribution in FIG. 8, it is clear that, in the crystal vibrationelement, the vibrational displacement is not confined to inside avibration region of a first part 242, and therefore the vibrationaldisplacements of second parts 252 are large compared with those of thesecond parts 250 in FIG. 6 or the second parts 251 in FIG. 7.

Here, the crystal vibration element is used by being held inside asealed space of a holder (for example, refer to FIG. 2). Generally, thecrystal vibration element is held by conductive holding members that areprovided on a substrate, which is a constituent element of the holder.Therefore, it is likely that vibration leakage will occur in whichvibration energy of the crystal vibration element leaks to the substratevia the conductive holding members. Consequently, if it is possible tosupport the crystal vibration element using conductive holding membersat a part of the crystal vibration element where the vibrationaldisplacement is substantially small, vibration leakage to the substratecan be reduced. Furthermore, if the area of the part where thevibrational displacement is substantially small is small, it is notpossible to secure this area within the holding areas of the conductiveholding members and the strength with which the crystal vibrationelement is held is reduced. As a result, stress is generated between thecrystal vibration element and the conductive holding members due tofalling impacts or deterioration that occurs over time, and cracking orpeeling off are likely to occur. Regarding this point, in contrast tothe comparative example illustrated in FIG. 8, the non-vibration regionscan be arranged over substantially the entirety of the second parts inthe embodiment of the present invention illustrated in FIGS. 6 and 7.Therefore, the embodiment of the present invention illustrated in FIGS.6 and 7 has effects of reducing vibration leakage, and reducing crackingor peeling off generated between the crystal vibration element and theconductive holding members.

FIG. 5 illustrates an example in which the thickness of the entirety ofeach second part 250 is smaller than the thickness of the first part 240of the vibration region.

The crystal vibration element is not limited to the above-describedconfiguration, and as a fourth modification described hereafter andillustrated in FIG. 10, a configuration may be used that includes afirst part 243 having a thickness T, second parts 253 that are adjacentto the first part 243 at the two ends of the first part 243 in the Xaxis direction, and third parts 263 that are adjacent to the secondparts 253 on the opposite sides from the first part 243, and in which athickness Tpe of the second parts 253 is smaller than the thickness T ofthe first part 243. In this case, the thickness T of the first part 243and a thickness Trm of the third parts 263 may be the same as eachother. In other words, a configuration may be used that has, in a sideview, groove portions (second parts 253) in parts that contact both endsof the vibration region in the X axis direction, the groove portionsbeing thinner than the other parts and extending in the seconddirection. In this case as well, the second parts 253 may serve asnon-vibration regions. In order to make it easier to grasp thedimensions of the crystal piece, illustration of the excitationelectrode provided on the main surface on the positive Y′ axis side,which is one of the pair of excitation electrodes provided with thethickness Tex in the vibration region of the crystal piece, is omittedfrom FIG. 10.

Patent Document 2 discloses a problem that if the thickness of aperipheral portion of a mesa shape is made small with respect to thethickness of a vibration region, a bending vibration is likely to beexcited in addition to a thickness shear vibration, and as a result, theeffect of energy confinement is reduced and size reduction is difficult.Specifically, in the case where the ratio between a thickness Tpe of theperipheral portion and a thickness T of the vibration region is 0.9,vibration energy leaks from the vibration region to the second parts, asin the comparative example in FIG. 8. However, by using theconfiguration according to the modification of the embodiment of thepresent invention, the energy confinement effect can be prevented frombeing degraded even when the ratio Tpe/T between the thicknesses of theperipheral portion and the vibration region is 0.9 or higher.

As yet another modification, although a configuration is illustrated inFIG. 5 in which the crystal piece has a mesa shape, a configuration mayinstead be adopted that includes a first part having a vibration region,and second parts that are adjacent to the two ends of the first part inthe X axis direction and that have substantially the same thickness asthe first part. In other words, as illustrated in FIG. 3, aconfiguration in which the crystal piece has a rectangularparallelepiped shape may also be implemented. In the case of thisconfiguration, once formula 1 above is satisfied, it is sufficient thatthe X axis direction length EL of the excitation electrodes thatgenerate the vibration region and the effective thickness Te bedetermined so as satisfy the following formula 3.EL/Te=1.603·n−0.292  Formula 3

With this configuration as well, it is considered that an effectequivalent to that of the configuration illustrated in FIG. 5 can beobtained.

FIGS. 9A and 9B illustrate a third modification, and illustratesimulation results for a mesa shape similar to that in FIG. 5. Theconditions in the third modification are W=0.277 mm, T=0.033 mm, L=0.77mm, EL=0.44 mm, D=0.0012 mm, Lt=0.165 mm, Tex=0.267 μm, and G/T=0,W/T=8.39, L/T=23.7, EL/T=12.8, Tpe/T=0.927.

FIGS. 10 to 11O illustrate a fourth modification. A crystal vibrationelement 216 illustrated in FIG. 10 includes a first part 243 having athickness T, second parts 253 that are adjacent to the first part 243 atthe two ends of the first part 243 in the X axis direction, and thirdparts 263 that are adjacent to the second parts 253 at the oppositesides from the first part 243, and the second parts 253 are thinner thanthe first part 243. Furthermore, the thicknesses of the first part 243and the third parts 263 are the same as each other. The thus-structuredcrystal vibration element 216 is held on the substrate by conductiveholding members at one of the third parts 263, for example. Theconditions in the fourth modification are W=0.277 mm, T=0.033 mm, L=0.77mm, EL=0.44 mm, D=0.0012 mm, Lt=0.11 mm, Lh=around 0.055 mm andTex=0.267 μm, and G/T=0, W/T=8.39, L/T=23.7 and EL/T=12.8. Lh iscalculated from the relational formula Lh≈(L−EL−2Lt)/2.

Next, vibration states of the crystal vibration element according to thefourth modification will be described while referring to FIGS. 11I to11O. FIGS. 11I to 11O illustrate simulation results of the vibrationdistribution for the front-surface side in the thickness direction, andillustrates vibration states that exist when the phase is shifted inunits of around 45° from a phase of 0° to around 225°. In each of thefigures, similarly to FIG. 11A, the magnitude of displacement isrepresented by being divided into ten gradations, and the lighter theshade of greyscale, the larger the amount of displacement. The phases ineach figure are approximate values. The positions of the points in themodels are displaced in proportion to the displacements in the vibrationdistribution.

FIG. 11I illustrates simulation results for a vibration state of a phaseof 0° in the case where the displacement is largest on the negative sidein the X direction of the simulation results (left side of screen). Asillustrated in FIG. 11I, there are three largest-displacement regions(regions having the brightest grayscale shade in FIG. 11I),specifically, there are a first region, a second region and a thirdregion located in a substantially central portion in the X direction.The first region is at the position of the long side on the negativeside in the Y direction, the second region is at a position shiftedtoward the positive side in the Y direction from the first region, andthe third region is at a position shifted toward the positive side inthe Y direction from the second region. The first region has asemi-elliptical shape obtained by vertically halving an ellipse having alongitudinal axe in the X axis direction. In addition, the second andthird regions have elliptical shapes having longitudinal axes thatextend in the X axis direction. The largest-displacement regionsillustrated in FIG. 11I are strong vibration regions that representamounts of displacement of 90% or more of the maximum amount ofdisplacement.

FIG. 11J illustrates simulation results for a phase of around 45°. InFIG. 11J, the largest value of displacement is reduced, and thepositions of the largest-displacement regions are shifted toward thepositive side in the X direction in response to this reduction, but themodel points (mesh) are the same as for a phase of 0°. The vibrationdistribution inclination is similar to that for a phase of 0°. Inaddition, the positions of the boundaries between the vibration regionand the non-vibration regions are substantially the same as those in thecase of a phase of 0°.

FIG. 11K illustrates simulation results for a phase of around 90°. Asthe phase advances, the largest values of displacement decrease further,and the positions of the largest-displacement regions are shiftedfurther toward the positive side in the X direction. In addition, thelength of the vibration region in the X direction gradually decreases asthe phase advances from a phase of 0°, and displacement does not appearover the entire front surface in the case where the phase is around 90°.

FIG. 11L illustrates simulation results for a phase of around 135°. Whenthe phase advances from a phase of around 90°, a vibration regionappears once again, and as the phase advances, the X direction length ofthe vibration region increases. At a phase of around 135°, the positionsof the largest-displacement regions are the inverse of those in the casewhere the phase is 45° with respect to the X direction.

FIG. 11M illustrates simulation results for a phase of around 180°. Asthe phase advances from around 135°, the largest values of displacementincrease, and at a phase of around 180°, the positions of thelargest-displacement regions are the inverse of those for a phase of 0°with respect to the X direction. The largest-displacement regionsillustrated in FIG. 11M are strong vibration regions that representamounts of displacement of 90% or more of the maximum amount ofdisplacement.

FIG. 11N illustrates simulation results for a phase of around 225°. Asthe phase advances from a phase of around 180°, the largest values ofdisplacement decrease, and the positions of the largest-displacementregions are shifted toward the negative side in the X direction. Inaddition, the positions of the largest-displacement regions aresubstantially the same for a phase of 0°, a phase of around 45°, a phaseof around 135°, a phase of around 180° and a phase of around 225°.

FIG. 11O illustrates simulation results for a phase of around 270°. Asthe phase advances, the largest values of displacement decrease further,and the positions of the largest-displacement regions are shiftedfurther toward the negative side in the X direction. In addition, thelength of the vibration region in the X direction gradually decreases asthe phase advances from a phase of 180°, and displacement does notappear over the entire front surface in the case where the phase isaround 270°.

As described above, it is clear from the transitions in the vibrationaldisplacement distribution that the vibration of this example hasantinodes, the specific positions of which are always points of maximumdisplacement, a vibration distribution in which displacement in thevicinity of the antinodes has a semi-elliptical or elliptical shape, andnodes at both ends in the X direction that are always points of smallestdisplacement, and it is clear that the crystal vibration elementvibrates with a stationary wave. In addition, the fact that thepositions of the points of maximum displacement appear to be differentfrom the positions of the antinodes at a phase of 0° and a phase ofabout 180° is because the positions of the individual parts of the modelare displaced positively and negatively in the various directions inaccordance with whether the generated displacements are positive ornegative in the various directions.

FIGS. 12A to 12D illustrate a comparative example. This comparativeexample is obtained by changing the numerical value of the length W ofthe short sides of the crystal piece of the fourth modification. Thatis, the conditions in the comparative example are W=0.260 mm, T=0.033mm, L=0.77 mm, EL=0.44 mm, D=0.0012 mm, Lt=0.11 mm, Lh=around 0.055 mmand Tex=0.267 μm, and G/T=0, W/T=7.88, L/T=23.7 and EL/T=12.8.

<Evaluation>

Next, the first modification, the third modification, the fourthmodification and the comparative example will be evaluated. FIG. 13illustrates a graph in which the vibration states in the firstmodification, the third modification, the fourth modification and thecomparative example are compared with each other. The XYZ axes of thesimulation model (corresponding to XZ′Y′ axes of crystal orientation)are referred to in the following description of the evaluation.

In FIG. 13, using the largest amplitude strength of the X directioncomponent (main vibration direction of thickness shear vibration) of aflat plate (without mesa shape) according to the first modification as areference, Z direction components are expressed as ratios with respectto this reference and ratios of the Z components with respect to thecorresponding X components are illustrated as percentages. FIG. 13illustrates the vibration distribution of a full-width thickness shearmode in a flat plate (first modification), the vibration distribution ofa full-width thickness shear mode in a mesa (third modification), thevibration distribution of a full-width thickness shear mode in asupported mesa (fourth modification) and the vibration distribution of anon-full-width thickness shear mode in a supported mesa. In the crystalvibration elements according to the first modification, the thirdmodification and the fourth modification, strong vibration regions thatrepresent a strength of 80% or more of the absolute value of the maximumstrength of the amplitude component of the X direction component arearrayed in the Y direction (Z′ direction of crystal orientation) and aredistributed in elliptical shapes that are elongated in the X direction,and when a main surface of the crystal piece is viewed in plan, thestrong vibration regions are not superposed with each other at the frontand rear main surfaces of the crystal piece and have opposite phasesfrom each other.

According to FIG. 13, the confinement state of the vibration region(mesa protruding portion) is improved and the amplitude strength of theX direction component is increased by 9% compared with the flat platedue to the mesa shape of the third modification. On the other hand, theZ (thickness) direction component increases from 0.11 to 0.14. It isthought that the cause of this is that the simulation model assumes thatthe crystal piece is subjected to etching processing, and rather thangiving the step portion a right angle shape, in order to take theanisotropy of etching due to the crystal orientation into consideration,the step portion is given a non-symmetrical shape in the X direction soas to have an inclination of 55° on the positive side of the stepportion in the X direction on the front main surface and an inclinationof 33° on the negative side of the step portion in the X direction, andtherefore a Z (thickness) direction vibration is excited as a subvibration of the X direction thickness shear vibration due to theasymmetry of the vibration.

Furthermore, with the supported mesa according to the fourthmodification, the confinement state of the vibration region (mesaprotruding portion) is improved and the amplitude strength of the Xdirection component is increased by 8% compared with the flat plate. Inaddition, it is thought that the vibration strength of the Z directioncomponent is reduced due to the symmetry of the shape of the stepportion being improved by increasing the thickness of the supportportions (non-vibration portions), which are the third parts 263 (referto FIG. 10). On the other hand, although the mass is increased due tothe increased thickness of the support portions, the vibration strengthof the X direction component is increased by 8% to 1.08 compared to theflat plate, and a decrease in the vibration strength of the X directioncomponent of the mesa having a small mass is limited to just 0.01 from1.09.

Furthermore, in the case of the supported mesa according to thecomparative example, the confinement state of the vibration region (mesaprotruding portion) is reduced and the amplitude strength of the Xdirection component is reduced by 6% compared with the flat plate. Inaddition, a vibration of a Z (thickness) direction component is excitedas a sub-vibration of the X direction thickness shear vibration, and thevibration strength of the Z (thickness) direction component greatlyincreases to 0.45 and the ratio of the Z (thickness) direction componentto the X direction component increases to 47.6%. This is thought to bebecause the X direction bending vibration is not confined to thethickness shear vibration region, and in addition to the thickness shearvibration having a main vibration in the X direction component, abending vibration having a main vibration in a Z direction (thickness)component is not confined to a mesa protruding portion, and theconcentration of energy in the thickness shear vibration is reduced.

In addition, in order to evaluate vibration leakage into the supportportions in the case of a supported mesa, the ratio of the maximumdisplacement of thick support portions (flanges) provided at the twoends of the crystal piece in the first direction with respect to themaximum displacement inside the vibration region was obtained (notillustrated). This ratio was 0.03 in the case of the fourthmodification, and 0.17 in the case of simple thickness shear vibration,that is, non-full-width thickness shear vibration, in the comparativeexample (W/T=7.88). Thus, compared with the simple thickness shearvibration, an effect can be obtained in that non-vibration regions arenot provided on both sides of the excitation electrodes of the crystalpiece in the width direction vibration and vibration leakage from thevibration region can be reduced by implementing full-width thicknessshear vibration.

Next, a fifth modification of a crystal vibration element 60 will bedescribed while referring to FIG. 14. Hereafter, points that aredifferent from the above-described content will be described.

The crystal vibration element 60 includes a crystal piece 61, a firstexcitation electrode 64 a that is provided on a first surface 62 a(front surface), which a main surface, of the crystal piece 61, and asecond excitation electrode 64 b that is provided on a second surface 62b (rear surface), which is a main surface, of the crystal piece 61 thatopposes the first surface 62 a.

In this example, when the XZ′ plane is viewed in plan, the short side ofthe first excitation electrode 64 a on the positive Z′ axis directionside is provided so that there is a gap between the short side of thefirst excitation electrode 64 a and the long side of the crystal piece61 on the positive Z′ axis direction side. In addition, the short sideof the first excitation electrode 64 a on the negative Z′ axis directionside is provided so that there is a gap between the short side of thefirst excitation electrode 64 a and the long side of the crystal piece61 on the negative Z′ axis direction side.

In addition, similarly for the second excitation electrode 64 b, whenthe XZ′ plane is viewed in plan, the short side of the second excitationelectrode 64 b on the positive Z′ axis direction side is provided sothat there is a gap between the short side of the second excitationelectrode 64 b and the long side of the crystal piece 61 on the positiveZ′ axis direction side. In addition, the short side of the secondexcitation electrode 64 b on the negative Z′ axis direction side isprovided so that there is a gap between the short side of the secondexcitation electrode 64 b and the long side of the crystal piece 61 onthe negative Z′ axis direction side.

In other words, the two short sides of the first excitation electrode 64a are provided on the first surface 62 a of the crystal piece 61 so thatthere are gaps between the short sides of the first excitation electrode64 a and the two long sides of the crystal piece 61. In addition, thetwo short sides of the second excitation electrode 64 b are provided onthe second surface 62 b of the crystal piece 61 so that there are gapsbetween the short sides of the second excitation electrode 64 b and thetwo long sides of the crystal piece 61. A size G of these gaps is 0<G≤20μM, for example. The size G of the gaps from the ridgelines of the sidesurfaces in the X direction preferably falls within a range in which anelectric field is applied to the Z′ axis direction side surfaces of thecrystal piece 61 by an alternating electric field applied between thefirst excitation electrode 64 a and the second excitation electrode 64b.

The size G of the gaps is preferably substantially uniform along thesides of the excitation electrodes. Furthermore, the sizes G of the gapsare preferably substantially the same at one side and the other side ofthe first excitation electrode 64 a, and the sizes G of the gaps arepreferably substantially the same at one side and the other side of thesecond excitation electrode 64 b. As a modification, the size G of thegaps may be different along parts of the sides of the excitationelectrodes. In addition, the sizes of the gaps G may be different alongthe one side and the other side of either of the first excitationelectrode 64 a and the second excitation electrode 64 b.

In this modification as well, a vibration mode is generated in which themain vibration is a thickness shear vibration generated when analternating electric field of a prescribed oscillation frequency, forexample, the AT-cut fundamental oscillation frequency, is applied, andthe vibration distribution of this vibration mode is substantially thesame as in the content described above on the basis of FIG. 4A. Inaddition, in this modification as well, when the XZ′ plane is viewed inplan, the vibration region extends in a band-like shape in the Z′ axisdirection of the crystal piece 61 similarly to the vibration region 40illustrated in FIG. 4A, and extends beyond the two short sides of thefirst excitation electrode 64 a and the second excitation electrode 64 billustrated in FIG. 14 toward the outside. In other words, the vibrationregion formed by the first excitation electrode 64 a and the secondexcitation electrode 64 b in FIG. 14 has a band-like shape that extendsin a continuous manner from one long side of the crystal piece 61 thatis parallel to the X axis direction to the other long side of thecrystal piece 61 that is similarly parallel to the X axis direction. Inthis modification as well, the non-vibration regions 50 a and 50 billustrated in FIG. 4A are adjacent to the two sides of the vibrationregion in the X axis direction of the crystal piece 61.

In addition, a connection electrode 66 a that is electrically connectedto the first excitation electrode 64 a via an extension electrode 65 aand a connection electrode 66 b that is electrically connected to thesecond excitation electrode 64 b via an extension electrode 65 b areformed on the crystal piece 61.

As described above, in the modification of this embodiment as well,excellent vibration characteristics can be obtained as a result of afull-width thickness shear mode being generated along the Z′ axisdirection of the crystal piece 61.

Second Embodiment

Next, a crystal vibrator 2 according to a second embodiment of thepresent invention will be described while referring to FIGS. 15 and 16.Here, FIG. 15 is an exploded perspective view of the crystal vibrator 2,and FIG. 16 is a sectional view taken along line XVI-XVI in FIG. 15.This embodiment differs from the first embodiment in terms of the formof the packaging of the crystal vibrator 2, and the same configurationsas in the first embodiment can be used for a crystal piece 102 of acrystal vibration element 110 and for the shapes, dimensions andpositional relationship of a first excitation electrode 114 a and asecond excitation electrode 114 b of the crystal vibration element 110.Hereafter, the points that are different from the content of the firstembodiment will be described.

As illustrated in FIG. 15, the crystal vibrator 2 according to thisembodiment includes the crystal vibration element 110, a first substrate120 and a second substrate 130.

In this modification, the first and second substrates 120 and 130 form acase or package for accommodating the crystal piece 102 of the crystalvibration element 110. The crystal vibration element 110, the firstsubstrate 120 and the second substrate 130 have substantially the samedimensions and shape (rectangular shape) as each other in the XZ′ plane.In the case where a manufacturing method is adopted in whichmanufacturing is performed up to step of packaging the crystal pieceswith the elements still in a wafer state such as wafer level chip sizepackaging “WLCSP”, a three-layer structure made up of a wafercorresponding to the first substrate 120, a wafer corresponding to thecrystal vibration element 110 and a wafer corresponding to the secondsubstrate 130 are processed together in one batch, and then thestructure is divided into individual crystal vibrators 2 using a dicingsaw. Therefore, the crystal vibration element 110, the first substrate120 and the second substrate 130 have substantially the same dimensionsand shape.

The crystal vibration element 110 includes the crystal piece 102, aframe body 104 that surrounds the periphery of the crystal piece 102,and connection members 118 a and 118 b that connect the crystal piece102 and the frame body 104 to each other. The frame body 104 is anexample of a support body that is for supporting the crystal piece 102.The crystal piece 102, the frame body 104 and the connection members 118a and 118 b are formed of a crystal material having a prescribed crystalorientation, for example, are formed of an AT-cut crystal material.

The thickness of the crystal vibration element 110 in the Y′ axisdirection is not particularly limited, and, for example, as illustratedin FIG. 16, the crystal piece 102, the frame body 104 and the connectionmembers 118 a and 118 b may all have the same thickness. Alternatively,a structure that is similar to a mesa structure may be adopted by makingthe thicknesses of the connection members 118 a and 118 b smaller thanthat of the crystal piece 102 in order to improve the confinement ofvibration energy.

The crystal vibration element 110 has long sides that extend in the Xaxis direction, short sides that extend in the Z′ axis direction and athickness in the Y′ axis direction. In the example illustrated in FIG.15, the connection members 118 a and 118 b are each arranged at one endof the long sides of the crystal piece 102 in the X axis direction. Thecrystal piece 102 is provided so as to be separated from the frame body104, and the crystal piece 102 and the frame body 104 are connected toeach other by the connection members 118 a and 118 b. In the exampleillustrated in FIG. 15, two connection members that are arranged at oneend of the long sides are illustrated, but the number of connectionmembers, the arrangement of the connection members and so forth are notparticularly limited. For example, one connection member that isarranged at one end of the long sides may be used as a connectionmember, or one of two connection members may be arranged at one end ofthe long sides and the other of the two connection members may bearranged at the other end of the long sides.

The crystal vibration element 110 has notched side surfaces 108 a, 108b, 108 c and 108 d that are formed by cutting away part of each cornerto form a cylindrical curved surface shape. In addition, similarly,notched side surfaces 122 a, 122 b, 122 c and 122 d are formed in thefirst substrate 120, and notched side surfaces 132 a, 132 b, 132 c and132 d are formed in the second substrate 130. These notched sidesurfaces are formed when a manufacturing method is adopted in whichmanufacturing is performed up to the packaging stage with the elementsstill in a wafer state such as WLCSP. In this case, for example, thenotched side surfaces 108 a, 122 a and 132 a among the notched sidesurfaces of the crystal vibration element 110, the first substrate 120and the second substrate 130 are formed in one go in the Y′ axisdirection. In addition, the shape of the notched side surfaces may be ashape other than a cylindrical curved surface shape, or alternativelysuch notches do not necessarily have to be formed.

The first and second excitation electrodes 114 a and 114 b arerespectively formed on the front and rear surfaces of the crystal piece102. The first excitation electrode 114 a is provided on a first surface112 a (front surface) of the crystal piece 102, and the secondexcitation electrode 114 b is provided on a second surface 112 b (rearsurface), which opposes the first surface 112 a, of the crystal piece102. The first and second excitation electrodes 114 a and 114 b arearranged as a pair of electrodes so as to be substantially entirelysuperposed with each other with the crystal piece 102 interposedtherebetween when the XZ′ plane is viewed in plan. The excitationelectrodes 114 a and 114 b have a rectangular shape in the XZ′ plane,and for example, are provided such that the long sides of the excitationelectrodes are parallel to the short sides of the crystal piece 102 andsuch that the short sides of the excitation electrodes are parallel tothe long sides of the crystal piece 102, as illustrated in FIG. 15.

An extension electrode 115 a, which is electrically connected to thefirst excitation electrode 114 a, is formed on a first surface 111 a ofthe frame body 104. The extension electrode 115 a extends from the firstexcitation electrode 114 a along one connection member 118 a, thenextends toward the notched side surface 108 a along the first surface111 a of the frame body 104, and is electrically connected to aconnection electrode 116 a that is formed on a second surface 111 b ofthe frame body 104. On the other hand, an extension electrode 115 b,which is electrically connected to the second excitation electrode 114b, is formed on the second surface 111 b of the frame body 104. Theextension electrode 115 b extends from the second excitation electrode114 b along the other connection member 118 b, and then extends towardthe notched side surface 108 b in the corner along the second surface111 b of the frame body 104, and is electrically connected to aconnection electrode 116 b that is formed on the second surface 111 b ofthe frame body 104. Thus, the connection electrodes 116 a and 116 b,which are electrically connected to the first and second excitationelectrodes 114 a and 114 b, are arranged at opposite corners of theframe body 104 in the example illustrated in FIG. 15.

The arrangement of the connection electrodes 116 a and 116 b, which areelectrically connected to the first and second excitation electrodes 114a and 114 b, is not particularly limited, and for example, theconnection electrodes 116 a and 116 b may be arranged at two corners ofthe frame body 104 on the negative X axis direction side, that is, atthe notched side surfaces 108 d and 108 b.

The first and second excitation electrodes 114 a and 114 b, theextension electrodes 115 a and 115 b, and the connection electrodes 116a and 116 b, for example, may be formed by forming a chromium (Cr) layeras a base layer and forming a gold (Au) layer on the surface of thechromium layer, but the electrodes are not limited to these materials.

The first substrate 120 is arranged on the first surface 112 a side ofthe crystal piece 102. The second substrate 130 is arranged on thesecond surface 112 b side of the crystal piece 102. In other words, thefirst substrate 120, the crystal vibration element 110 and the secondsubstrate 130 are stacked on top of one another in this order and form athree-layer structure. The second substrate 130 has an installationsurface on which the crystal vibration element 110 is installed, and amounting surface that opposes the installation surface and iselectrically connected to the outside.

Outer electrodes 134 a, 134 b, 134 c and 134 d are formed at the cornersof the mounting surface of the second substrate 130. When the crystalvibration element 110 is mounted on the second substrate 130, the outerelectrode 134 a is electrically connected to the first excitationelectrode 114 a via the connection electrode 116 a and the extensionelectrode 115 a. In this way, the outer electrode 134 b is electricallyconnected to the second excitation electrode 114 b via the connectionelectrode 116 b and the extension electrode 115 b. The remaining outerelectrodes 134 c and 134 d are dummy electrodes that are notelectrically connected to either of the first and second excitationelectrodes 114 a and 114 b. The details of the dummy electrodes are thesame as already described.

Although the outer electrodes 134 a and 134 b, which are electricallyconnected to the first and second excitation electrodes 114 a and 114 b,are arranged at opposite corners of the second substrate 130 in theexample illustrated in FIG. 15, the outer electrodes 134 a and 134 b arenot limited to this arrangement and may instead be arranged at othercorners. In addition, in the case wherecylindrical-curved-surface-shaped notched side surfaces are formed atthe corners of the second substrate 130, the outer electrodes may extendfrom the mounting surface of the second substrate 130 so as to reach thenotched side surfaces in the corresponding corners.

The outer electrodes 134 a to 134 d are formed of chromium (Cr) and gold(Au), for example. A sputtering method or a plating method may be usedas a method to form the electrodes. Although a four-terminal structuremade up of four outer electrodes is described in this embodiment, thenumber of outer electrodes is not particularly limited, and atwo-terminal structure made up of two outer electrodes may be used, forexample.

The first and second substrates 120 and 130 are planar substrates. Inaddition, the first and second substrates 120 and 130 may be formed of aglass material (for example, a material having silicate glass as a maincomponent or a material having a main component other than silicate, andexhibiting a glass transition phenomenon with an increase intemperature), or may be formed of the same crystal material as thecrystal vibration element 110 (for example, AT-cut crystal).

As illustrated in FIGS. 15 and 16, the first substrate 120 is bonded tothe entire periphery of the first surface 111 a of the frame body 104via a first bonding material 140, and the second substrate 130 is bondedto the entire periphery of the second surface 111 b of the frame body104 via a second bonding material 142. The crystal piece 102 ishermetically sealed in an internal space (cavity) 123 as a result of thefirst and second bonding materials 140 and 142 being provided along theentire peripheries of the surfaces of the frame body 104. It issufficient that the first and second bonding materials 140 and 142 beable to bond bonding surfaces of the respective members and form aninternal space, and the materials of the first and second bondingmaterials 140 and 142 are not limited. The first and second bondingmaterials 140 and 142 may be formed of a glass adhesive material such asa low-melting-point glass (for example, a lead boric acid based orphosphoric acid based glass), or an resin adhesive may be used.

The content described in the first embodiment above (refer to FIGS. 1 to14) may be applied to the configurations of the crystal piece 102, thefirst excitation electrode 114 a and the second excitation electrode 114b of the crystal vibration element 110 according to this embodiment.With the crystal vibrator 2 according to this embodiment, excellentvibration characteristics can be obtained as a result of a full-widththickness shear mode being generated along the Z′ axis direction of thecrystal piece 102.

Third Embodiment

A crystal vibrator according to an embodiment of the present inventionwill be described while referring to FIGS. 17 and 18. Here, FIG. 17 isan exploded perspective view of the crystal vibrator, and FIG. 18 is asectional view taken along line XVIII-XVIII in FIG. 17. Illustration ofvarious electrodes of a crystal vibration element is omitted from FIG.18.

Hereafter, the configuration of the crystal vibrator according to thisembodiment will be described. Unless whatever is described hereaftercontradicts the content described in embodiments 1 and 2, the contentdescribed in embodiments 1 and 2 may be selectively applied asappropriate.

As illustrated in FIG. 17, a crystal vibrator 1001 according to thisembodiment includes a crystal vibration element 1100, a cap 1200 and asubstrate 1300. The cap 1200 and the substrate 1300 form a holder (caseor package) that accommodates the crystal vibration element 1100.

The crystal vibration element 1100 includes a crystal piece 1110, andexcitation electrodes 1120 and 1130 (hereafter, also referred to as“first and second excitation electrodes 1120 and 1130”) that arerespectively provided on the front and rear surfaces of the crystalpiece 1110. The first excitation electrode 1120 is provided on a firstsurface 1112 (front surface), which is a main surface, of the crystalpiece 1110. The second excitation electrode 1130 is provided on a secondsurface 1114 (rear surface), which is a main surface that opposes thefirst surface 1112, of the crystal piece 1110.

Regarding the configuration of crystal piece 1110 in terms of thecrystal structure, cut angle and so on, the content described for thecrystal piece 11 in the first embodiment can be applied to the crystalpiece 1110. In the example illustrated in FIG. 17, the crystal piece1110 is an AT-cut crystal piece. The AT-cut crystal piece 1110 has longsides that are parallel to the X axis, short sides that are parallel tothe Z′ axis and a thickness that is parallel to the Y′ axis. Hereafter,the long sides may be referred to as a longitudinal direction, the shortsides may be referred to as a lateral direction, and the thickness maybe referred to as a thickness direction. Furthermore, the AT-cut crystalpiece 1110 has a rectangular shape when the XZ′ plane is viewed in plan.

The crystal piece according to this embodiment is not limited to theabove-described configuration, and for example, an AT-cut crystal piecehaving long sides that are parallel to the Z′ axis and short sides thatare parallel to the X axis direction may be used instead. Alternatively,provided that the main vibration is the thickness shear mode, thecrystal piece may be a crystal piece having a different kind of cut froman AT cut such as a BT cut, for example.

The first excitation electrode 1120 is formed on the first surface 1112(XZ′ surface on positive Y′ axis direction side) of the crystal piece1110, and the second excitation electrode 1130 is formed on the secondsurface 1114 (XZ′ surface on negative Y′ axis direction side), which ison the opposite side from the first surface 1112, of the crystal piece1110. The first and second excitation electrodes 1120 and 1130 arearranged as a pair of electrodes having the crystal piece 1110interposed therebetween so as to be substantially entirely superposedwith each other when the XZ′ plane is viewed in plan. The first andsecond excitation electrodes 1120 and 1130 have a rectangular shape inthe XZ′ plane. In addition, the first and second excitation electrodesare provided such that the long sides of the excitation electrodes areparallel to the long sides of the crystal piece 1110, and the shortsides of the excitation electrodes are parallel to the short sides ofthe crystal piece 1110. The details of the configurations of the crystalpiece 1110 and the excitation electrodes 1120 and 1130 will be describedlater.

A connection electrode 1124 that is electrically connected to the firstexcitation electrode 1120 via an extension electrode 1122, and aconnection electrode 1134 that is electrically connected to the secondexcitation electrode 1130 via an extension electrode 1132 are formed onthe crystal piece 1110. Specifically, the extension electrode 1122extends from the first excitation electrode 1120 toward the short sideon the negative X axis direction side on the first surface 1112, passesalong a side surface of the crystal piece 1110 on the negative X axisdirection side and is connected to the connection electrode 1124 formedon the second surface 1114. The extension electrode 1132 extends fromthe second excitation electrode 1130 toward the short side on thenegative X axis direction side on the second surface 1114, and isconnected to the connection electrode 1134 formed on the second surface1114. The connection electrodes 1124 and 1134 are arranged along theshort side on the negative X axis direction side, and the connectionelectrodes 1124 and 1134 are electrically connected to and mechanicallyheld by the substrate 1300 via conductive holding members 1340 and 1342,which will be described later. In this embodiment, the connectionelectrodes 1124 and 1134 and the extension electrodes 1122 and 1132 arenot limited to these arrangements and pattern shapes, and can be changedas appropriate by considering the electrical connections between theseelectrodes and other members.

The first and second excitation electrodes 1120 and 1130, the extensionelectrodes 1122 and 1132, and the connection electrodes 1124 and 1134may for example be formed by forming a chromium (Cr) layer as a baselayer and forming a gold (Au) layer on the surface of the chromiumlayer, but the electrodes are not limited to these materials.

As illustrated in FIG. 18, the cap 1200 has a recess 1204 that openstoward a first surface 1302 of the substrate 1300. The recess 1204 isprovided with a side wall portion 1202 that is formed so as to standupright from a bottom surface of the recess 1204 along the entireperiphery of the opening of the recess 1204, and the side wall portion1202 has an end surface 1205 that faces the first surface 1302 of thesubstrate 1300.

The material of the cap 1200 is not particularly limited, and may beformed of a metal, for example. Thus, a shielding function can be addedby electrically connecting the cap 1200 to the ground potential.Alternatively, the cap 1200 may be formed of an insulating material ormay have a composite structure made up of a metal and an insulatingmaterial.

As a modification, the cap 1200 may have a flange portion that protrudesfrom the side wall portion 1202 in a direction away from the opening.Thus, since the area of the bond between the cap 1200 and the substrate1300 can be increased by bonding the flange portion and the substrate1300 to each other, it is possible to improve the strength of the bondbetween the cap 1200 and the substrate 1300.

The crystal vibration element 1100 is mounted on the first surface 1302(upper surface) of the substrate 1300. In the example illustrated inFIG. 17, the substrate 1300 has long sides that are parallel to the Xaxis, short sides that are parallel to the Z′ axis, and a thickness thatis parallel to the Y′ axis, and has a rectangular shape in the XZ′plane. The substrate 1300 may be formed of an insulating ceramic forexample, and may be formed by stacking a plurality of insulating ceramicsheets on top of one another and then firing the insulating ceramicsheets. Alternatively, the substrate 1300 may be formed of a glassmaterial, a crystal material or a glass epoxy resin, for example. Thesubstrate 1300 is preferably formed of a heat-resistant material. Thesubstrate 1300 may be formed of a single layer or a plurality of layers,and in the case where the substrate 1300 is formed of a plurality oflayers, an insulating layer may be formed as the uppermost layer thatforms the first surface 1302. Furthermore, the substrate 1300 may have aflat-plate shape, or may have a concave shape that opens in a directionso to face the cap 1200. As illustrated in FIG. 15, the cap 1200 and thesubstrate 1300 are bonded to each other via a bonding material 1350, andas a result, the crystal vibration element 1100 is hermetically sealedin an internal space (cavity) 1206 enclosed by the recess 1204 of thecap 1200 and the substrate 1300.

The bonding material 1350 is provided along the entire peripheries ofthe cap 1200 and the substrate 1300, and is interposed between the endsurface 1205 of the side wall portion 1202 of the cap 1200 and the firstsurface 1302 of the substrate 1300. The bonding material 1350 iscomposed of an insulating material. The insulating material may be aglass material (for example, a low-melting-point glass), or may be aresin material (for example, an epoxy resin), for example. Thesesinsulating materials have a low melting point and low cost compared witha metal material. Therefore, the heating temperature used in the step ofbonding the cap 1200 and the substrate 1300 to each other by can besuppressed by using such an insulating material for the bonding material1350, and a reduction in the cost of the crystal vibrator can beachieved.

In the example illustrated in FIG. 18, one end of the crystal vibrationelement 1100 (end portion on conductive holding members 1340 and 1342side) is a fixed end, and the other end of the crystal vibration element1100 is a free end. As a modification, the crystal vibration element1100 may be fixed to the substrate 1300 at both ends thereof in thelongitudinal direction.

As illustrated in FIG. 17, the substrate 1300 includes connectionelectrodes 1320 and 1322 that are formed on the first surface 1302, andextension electrodes 1320 a and 1322 a that extend from the connectionelectrodes 1320 and 1322 toward an outer edge of the first surface 1302.The connection electrodes 1320 and 1322 are arranged inside the outeredge of the substrate 1300 such that the crystal vibration element 1100can be arranged substantially in the center of the first surface 1302 ofthe substrate 1300.

The connection electrode 1124 of the crystal vibration element 1100 isconnected to the connection electrode 1320 via the conductive holdingmember 1340, and the connection electrode 1134 of the crystal vibrationelement 1100 is connected to the connection electrode 1322 via theconductive holding member 1342.

The extension electrode 1320 a extends from the connection electrode1320 to any corner of the substrate 1300, and the extension electrode1322 a extends from the connection electrode 1322 to another corner ofthe substrate 1300. In addition, a plurality of outer electrodes 1330,1332, 1334 and 1336 are formed at the corners of the substrate 1300. Inthe example illustrated in FIG. 17, the extension electrode 1320 a isconnected to the outer electrode 1330 formed at the corner on thepositive Z′ axis direction side and negative X axis direction side, andthe extension electrode 1322 a is connected to the outer electrode 1332formed at the corner on the negative Z′ axis direction side and positiveX axis direction side. In addition, as illustrated in FIG. 17, the outerelectrodes 1334 and 1336 may be formed at the remaining corners. Theseouter electrodes may be used as dummy electrodes as already describedabove. In this case, a shielding function may be added to the cap 1200by electrically connecting the cap 1200, which is composed of aconductive material, to the outer electrodes 1334 and 1336 serving asdummy electrodes.

In the example illustrated in FIG. 17, the corners of the substrate 1300each have a notched side surface that is formed by cutting away part ofthe corner to form a cylindrical curved surface shape, and the outerelectrodes 1330, 1332, 1334 and 1336 are each formed so as to extendacross the first surface 1302, the notched side surface and a secondsurface 1304 in a continuous manner. The corners of the substrate 1300are not limited to having this shape, and the notched shape may be aplanar shape, or the four corners may have a right-angle rectangularshape in plan view without having a notch.

The configurations of the connection electrodes, the extensionelectrodes and the outer electrodes of the substrate 1300 are notlimited to the above-described examples and may be modified and used invarious ways. For example, the connection electrodes 1320 and 1322 maybe arranged on different sides of the first surface 1302 of thesubstrate 1300 such as one being formed on the positive X axis directionside and the other being formed on the negative X axis direction side.In this configuration, the crystal vibration element 1100 would besupported by the substrate 1300 at both one end and the other endthereof in the longitudinal direction. In addition, the content alreadydescribed above can be applied to the number and arrangement of theouter electrodes, the presence/absence of dummy electrodes, and the formof the electrical connections between the outer electrodes and theconnection electrodes.

In the crystal vibrator 1001 illustrated in FIG. 17, analternating-current voltage is applied between the pair of first andsecond excitation electrodes 1120 and 1130 of the crystal vibrationelement 1100 via the outer electrodes 1330 and 1332, and as a result,the crystal piece 1110 undergoes vibration with the main vibrationthereof being a thickness shear vibration, and resonance characteristicsare obtained along with the vibration.

Next, the crystal vibration element illustrated in FIG. 17 will bedescribed in more detail while referring to FIGS. 19 to 21. FIG. 19illustrates the crystal piece and the excitation electrode on the firstsurface thereof of the crystal vibration element illustrated in FIG. 17(illustration of the extension electrodes and the connection electrodesis omitted for ease of description). FIGS. 20A and 20B are graphs fordescribing the characteristics of the crystal vibration element. FIG. 21is an equivalent circuit diagram of the crystal vibration element.

As illustrated in FIG. 19, a long side 1120 a of the excitationelectrode 1120 on the positive Z′ axis direction side is parallel to along side 1112 a of the crystal piece 1110 on the positive Z′ axisdirection side, and the crystal vibration element has a relation of0.0002≤G/T≤0.5, where G is the distance between the long side 1120 a ofthe excitation electrode 1120 and the long side 1112 a of the crystalpiece 1110, and T is the thickness of the crystal piece 1110 between theexcitation electrodes 1120 and 1130. In other words, the long side 1120a of the excitation electrode 1120 is spaced apart from the long side1112 a of the crystal piece 1110 toward the inside by the distance andthis distance G has a relational formula with respect to the thickness Tof the crystal piece 1110.

Thus, since there is a risk of the quality of the material changing dueto the sides of the main surfaces of the crystal piece 1110 being likelyto be damaged during the manufacturing process, degradation of thevibration characteristics caused by such damage can be suppressed bysetting a lower limit for the above relational formula. On the otherhand, if the distance G is made too large, a wasted area that does notcontribute to vibration increases, and therefore an effective area issecured for the excitation electrodes while facilitating size reductionof the crystal vibration element by setting an upper limit for the aboverelational formula.

In addition, it is clear that the crystal vibration element hasexcellent vibration characteristics when the capacitance ratio of anequivalent circuit of the crystal vibration element is small. In otherwords, as illustrated in FIG. 21, it is known that the frequencysensitivity of the crystal vibration element can be made high if thecapacitance ratio C0/C1=γ is small in an equivalent circuit of thecrystal vibration element in which an equivalent series resistance R1,an equivalent series capacitance C1 and an equivalent series inductanceL1 are connected in series with each other, and an equivalent parallelcapacitance C0 is connected in parallel with the series circuit.

Regarding this point, if we look at the relationship between G/T and thecapacitance ratio γ using FIGS. 20A and 20B, it is clear that there is acritical point where the rate of increase of the capacitance ratio γbecomes high at around G/T=0.5 as illustrated in FIG. 20A, and that thecapacitance ratio γ varies and becomes large when G/T is less than0.0002 and in the vicinity of 0.0001 as illustrated in FIG. 20B (rangeof FIG. 20A illustrated where G/T is close to zero). In other words, itis clear that the capacitance ratio γ can be made small as a result ofG/T having the above relational formula. The frequency sensitivity ofthe crystal vibration element can be made high by making the capacitanceratio γ small, and excellent vibration characteristics can be obtainedby improving frequency controllability of the crystal vibration elementin this way. In addition, if the excitation electrode is provided withrespect to the end surface of the crystal piece such that G/T is lessthan 0.0002, there is an effect that the shape of the end surface of thecrystal piece becomes unstable in addition to the effect of variationsin the capacitance ratio γ. Therefore, it preferable that the excitationelectrode be provided on the crystal piece such that G/T is 0.0002 orhigher.

Furthermore, as illustrated in FIG. 20A, from the fact that there is acritical point at which the rate of increase of the capacitance ratio γincreases at around G/T=0.2 (between 0.2 and 0.3), it is furtherpreferable that the crystal vibration element have a relation ofG/T≤0.2.

In order to set the capacitance ratio γ to be small and stable, it iseven more preferable that the crystal vibration element have a relationof 0.0002≤G/T≤0.2.

The relational formula for G/T described above similarly applies to therelationship between a long side 1120 b of the excitation electrode 1120on the negative Z′ axis direction side and a long side 1112 b of thecrystal piece 1110 on the negative Z′ axis direction side. Furthermore,although the excitation electrode 1120 on the first surface 1112 of thecrystal piece 1110 is described above, the description similarly appliesto the long sides on the second surface 1114 side of the crystal piece1110. The above relational formula is applied to the long sides of thecrystal piece 1110 rather than the short sides of the crystal piece 1110because there is a greater effect on the vibration characteristics ofthe crystal piece in the case where the distance to the long sides isrelatively large.

In addition, the crystal piece 1110 may have a relation of W/T 10.2,where W is the width of the short sides of the crystal piece 1110.Hereafter, the technical significance of this relational formula will beexplained.

In the crystal vibration element, in addition to the main vibration,resonance is generated due to spurious (unwanted vibration) caused bythe shape, dimensions and so on of the crystal vibration element. Thisresonance due to spurious appears as dips (troughs), which may be largeor small, in the impedance curve. If such a dip is close to the mainvibration, it is possible that the crystal vibration element will beadversely affected such as the oscillation frequency being shifted andthe oscillation margin being reduced due to an increase in resonantresistance. Here, in a rectangular crystal vibration element such as thecrystal vibration element of this embodiment, the spurious is a widthvibration related to W/T where W is the width of the short sides and Tis the thickness of the crystal piece, and a plurality of suchvibrations exist as a plurality of modes of different orders. Suchspurious is called width spurious. Looking at a case where the widthspurious is close to the main vibration, when W is small, the frequencyinterval between the width spurious components is large as illustratedin FIG. 22A, and conversely, when W is large, the frequency intervalbetween the width spurious components is small as illustrated in FIG.22B. In addition, looking at variations that occur as the temperaturechanges, in an AT-cut crystal piece, the main vibration varies in theform of a cubic function as the temperature changes from 0° C. to 50° C.for example, and more specifically varies in a range of around 10 ppm,whereas the width spurious varies in the form of a linear function suchthat the value thereof becomes smaller and more specifically varies byaround 1.0%. Variations in the main vibration can be relatively ignoredwhen compared with the variations that occur in the width spurious withchanges in temperature.

Referring to FIG. 23, values of W/T at which there is little effect onspurious vibration with changes in temperature will be described. Here,FIG. 23 is a graph in which the horizontal axis represents W/T and thevertical axis represents ΔF/ΔP (spurious density). The temperature ischanged from 0° C. to 50° C., which is the main use temperature range ofelectronic devices.

FIG. 23 will be specifically described. First, using finite elementanalysis, the generation frequencies and number of width spuriouscomponents at frequencies around the main vibration was investigated byvarying W/T at a normal temperature, and the average frequency intervalΔP (MHz) between adjacent spurious components was calculated. Inaddition, an analysis was performed by extracting W=430 (W/T=10.35) anda frequency of 37.4 MHz as one set of conditions, and varying thetemperature from 0° C. to 50° C. From the results of the analysis, theamount of variation of a spurious component when the temperature wasvaried from 0° C. to 50° C. was calculated for ten width spuriouscomponents around the main vibration, and the average value ΔF (MHz)thereof was calculated. In other words, the frequency of a spuriouscomponent has a variation width ΔF for each value of W/T that depends onchanges in temperature. If the frequency interval ΔP between two widthspurious components between which the frequency of the main vibration isinterposed is smaller than ΔF, it is possible that at least one of theadjacent width spurious components will cross over the main vibrationwith a change in temperature. Thus, at each value of W/T, there is ahigh possibility that a width spurious component will unavoidably crossover the main vibration when the frequency interval ΔP between adjacentwidth spurious components is small with respect to ΔF, and depending onthe case, there is also a possibility of a plurality of width spuriouscomponents crossing over the main vibration and of the characteristicsbeing markedly degraded. Accordingly, as illustrated in FIG. 23, atΔF/ΔP≤1, that is, the region of values of W/T smaller than the W/T atwhich the interval between two width spurious components that areadjacent to the main vibration matches the width of variation thatoccurs when the temperature is varied from 0° C. to 50° C. (that is,W/T≤10.2 as illustrated in FIG. 23), it is highly possible to design thecrystal vibration element such that a width spurious component does notcross over the main vibration, and more specifically, such that theexcitation frequency of the main vibration and the frequency of a widthspurious component do not coincide with each other, and the smaller thevalue of W/T, the lower the risk of a spurious component crossing overthe main vibration. The position of a spurious component can be variedsomewhat by subjecting the crystal piece to beveling or convexmachining. Consequently, in the range of W/T 10.2, it is possible tofurther reduce the risk of a width spurious component crossing over themain vibration by making the width dimension smaller in a pseudo mannerby subjecting the crystal piece to beveling or convex machining.

It is sufficient for the length L of the long sides of the crystal piece1110 to be appropriately chosen in accordance with the desired vibrationcharacteristics and so forth.

According to this embodiment, the above-described relationship betweenthe distance G between the long side 1112 a of the crystal piece 1110and the long side 1120 a of the excitation electrode 1120, and thethickness T of the crystal piece 1110 between the excitation electrodes1120 and 1130 is satisfied, and therefore excellent vibrationcharacteristics can be obtained as described above.

The present invention is not limited to the above-described embodimentand can be modified and used in various ways. In the followingdescription, points that are different from the above-described contentare described, and parts of the configuration that are the same as inthe above-described content are denoted by the same symbols in thedrawings.

Crystal vibration elements according to modifications of this embodimentwill be described while referring to FIGS. 24 to 26. In each of thefollowing modifications, the configuration of the crystal piece isdifferent from the above-described content.

FIG. 24 is a drawing for describing a crystal vibration elementaccording to a first modification, and this example includes a crystalpiece having a so-called mesa structure in the longitudinal direction.

A crystal piece 1410 of a crystal vibration element 1400 according tothis modification includes a vibration portion 1402 across whichexcitation electrodes 1420 and 1430 are superposed with each other, andthin end portions 1404 and 1406 that are connected to the vibrationportion 1402 and are formed so as to be thinner than the vibrationportion 1402. Similarly to as illustrated in FIG. 17, the crystal piece1410 has long sides that are parallel to the X axis and short sides thatare parallel to the Z′ axis, and the thin end portions 1404 and 1406 areprovided at the two ends of the crystal piece 1410 in the direction inwhich the long sides of the crystal piece 1410 extend. Furthermore, theexcitation electrode 1420 is formed on a first surface 1412, which isone main surface, of the vibration portion 1402, and the excitationelectrode 1430 is formed on a second surface 1414, which is another mainsurface, of the vibration portion 1402. The first and second surfaces1412 and 1414 of the vibration portion 1402 are each formed in arectangular shape that extends in a direction parallel to the X axisdirection.

In this modification as well, a long side 1420 a of the excitationelectrode 1420 on the positive Z′ axis direction side is parallel to along side 1412 a of the crystal piece 1410 on the positive Z′ axisdirection side, and the excitation electrode 1420 has the relationalformula for G/T described above, where G is the distance between thelong side 1420 a of the excitation electrode 1420 and the long side 1412a of the crystal piece 1410, and T is the thickness of the crystal piece1410 between the excitation electrodes 1420 and 1430. The relationalformula for G/T similarly applies to the relationship between a longside 1420 b of the excitation electrode 1420 on the negative Z′ axisdirection side and a long side 1412 b of the crystal piece 1410 on thenegative X axis direction side. In addition, the relational formula forG/T similarly applies to the long sides of the crystal piece 1410 on theexcitation electrode 1430 side of the crystal piece 1410.

According to this modification, the crystal piece 1410 has the thin endportions 1404 and 1406 that are formed at the two ends of the crystalpiece 1410 in the longitudinal direction so as to have a smallerthickness than the vibration portion 1402, and therefore, in addition tobeing able to obtain excellent vibration characteristics as describedabove, this modification also has operational effects that arecharacteristic of a mesa structure such as being excellent in terms ofconfinement of vibration energy.

FIG. 25 is a drawing for describing a crystal vibration elementaccording to a second modification, and this example includes a crystalpiece having a so-called mesa structure in the lateral direction.

A crystal piece 1510 of a crystal vibration element 1500 according tothis modification includes a vibration portion 1502 across which anexcitation electrode 1520 and an excitation electrode on the negative Y′axis direction side, which is not illustrated, are superposed with eachother, and thin end portions 1504 and 1506 that are connected to thevibration portion 1502 and are formed so as to thinner than thevibration portion 1502. Similarly to as illustrated in FIG. 17, thecrystal piece 1510 has long sides that are parallel to the X axis andshort sides that are parallel to the Z′ axis, and the thin end portions1504 and 1506 are provided at the two ends of the crystal piece 1510 inthe direction in which the short sides of the crystal piece 1510 extend.In addition, the excitation electrode 1520 is formed on a first surface1512, which is one main surface, of the vibration portion 1502, and anexcitation electrode on the negative Y′ axis direction side, which isnot illustrated, is formed on a second surface 1514, which is anothermain surface, of the vibration portion 1502. The first and secondsurfaces 1512 and 1514 of the vibration portion 1502 are each formed ina rectangular shape that extends in a direction parallel to the X axisdirection.

In this modification as well, a long side 1520 a of the excitationelectrode 1520 on the positive Z′ axis direction side is parallel to along side 1512 a of the crystal piece 1510 on the positive Z′ axisdirection side, and the excitation electrode 1520 has the relationalformula for G/T described above, where G is the distance between thelong side 1520 a of the excitation electrode 1520 and the long side 1512a of the crystal piece 1510, and T is the thickness of the crystal piece1510 between the excitation electrodes. The relational formula for G/Tsimilarly applies to the relationship between a long side 1520 b of theexcitation electrode 1520 on the negative Z′ axis direction side and along side 1512 b of the crystal piece 1510 on the negative Z′ axisdirection side. In addition, the relational formula for G/T similarlyapplies to the long sides of the crystal piece 1510 on an excitationelectrode 1530 side of the crystal piece 1510.

According to this modification, the crystal piece 1510 has the thin endportions 1504 and 1506 that are formed at the two ends of the crystalpiece 1510 in the lateral direction so as to have a smaller thicknessthan the vibration portion 1502, and therefore, in addition to beingable to obtain excellent vibration characteristics as described above,this modification also has operational effects that are characteristicof a mesa structure such as being excellent in terms of confinement ofvibration energy.

A mesa structure is not limited to the forms illustrated in FIGS. 24 and25, and a mesa structure obtained by combining the configurationsillustrated in FIGS. 24 and 25 may be adopted, for example. Thus, thecrystal piece can have thin end portions at both sides in thelongitudinal direction and the lateral direction and can have theoperational effects described for the forms illustrated in FIGS. 24 and25.

FIG. 26 is a drawing for describing a crystal vibration elementaccording to a third modification, and in this example, grooves areformed between end portions and a vibration portion of the crystalpiece.

A crystal piece 1610 of a crystal vibration element 1600 according tothis modification is provided with an excitation electrode 1620 on afirst surface 1612 thereof and an excitation electrode 1630 on a secondsurface 1614 thereof. The first and second excitation electrodes 1620and 1630 are provided so as to be superposed with each other with thecrystal piece 1610 interposed therebetween. The crystal piece 1610 has avibration portion 1602 across which the first and second excitationelectrodes 1620 and 1630 are superposed with each other. The crystalpiece 1610 has long sides that are parallel to the X axis and shortsides that are parallel to the Z′ axis, similarly to the exampleillustrated in FIG. 17. A first end portion 1604 is provided on thepositive X axis direction side in the direction in which the long sidesof the crystal piece 1610 extend, and a second end portion 1606 on thenegative X axis direction side, which the opposite side from the firstend portion 1604. That is, the vibration portion 1602 is providedbetween the first end portion 1604 and the second end portion 1606.

In the example illustrated in FIG. 26, grooves 1608 and 1609 arerespectively formed between the first end portion 1604 and the vibrationportion 1602 and between the second end portion 1606 and the vibrationportion 1602. These grooves 1608 and 1609 extend from one long side 1612a of the crystal piece 1610 to another long side 1612 b of the crystalpiece 1610. The grooves 1608 and 1609 are formed on the positive Y′direction side of the crystal piece 1610. As illustrated in FIG. 26,grooves may be similarly formed on the negative Y′ direction side of thecrystal piece 1610. The depth of the grooves 1608 and 1609 is notparticularly limited and should be appropriately set in order to obtainthe desired vibration characteristics. The cross sectional shapes of thegrooves 1608 and 1609 in a direction perpendicular to the direction inwhich the grooves 1608 and 1609 extend are not particularly limited, andmay be a recessed shape having a bottom surface as illustrated in FIG.26, or may be a V shape formed of two inclined side surfaces. Inaddition, the grooves 1608 and 1609 may have cross sectional shapes thatare uniform in the direction in which the grooves 1608 and 1609 extendas illustrated in FIG. 26, or the grooves 1608 and 1609 may have crosssectional shapes that vary, for example, have different groove widths.

The excitation electrode 1620 is formed on the first surface 1612, whichis one main surface, of the vibration portion 1602, and the excitationelectrode 1630 is formed on a second surface 1614, which is another mainsurface, of the vibration portion 1602. The first and second surfaces1612 and 1614 of the vibration portion 1602 are each formed in arectangular shape having long sides that are parallel to the X axis andshort sides that are parallel to the Z′ axis.

In this modification as well, a long side 1620 a of the excitationelectrode 1620 on the positive Z′ axis direction side is parallel to thelong side 1612 a of the crystal piece 1610 on the positive Z′ axisdirection side, and the excitation electrode 1620 has the relationalformula for G/T described above, where G is the distance between thelong side 1620 a of the excitation electrode 1620 and the long side 1612a of the crystal piece 1610, and T is the thickness of the crystal piece1610 between the excitation electrodes 1620 and 1630. The relationalformula for G/T similarly applies to the relationship between a longside 1620 b of the excitation electrode 1620 on the negative Z′ axisdirection side and the long side 1612 b of the crystal piece 1610 on thenegative Z′ axis direction side. In addition, the relational formula forG/T similarly applies to the long sides of the crystal piece 1610 on theexcitation electrode 1630 side of the crystal piece 1610.

According to this modification, the grooves 1608 and 1609 arerespectively formed between the first end portion 1604 and the vibrationportion 1602 and between the second end portion 1606 and the vibrationportion 1602, and therefore this modification exhibits the operationaleffects of a so-called mesa structure. In other words, in addition tobeing able to obtain excellent vibration characteristics as describedabove, this modification also has operational effects that arecharacteristic of a mesa structure such as being excellent in terms ofvibration energy confinement.

In the example illustrated in FIG. 26, a configuration is described inwhich two grooves are formed on the positive Y′ axis direction side, forexample. However, the grooves are not limited to this configuration, andthere may be one groove that extends in the direction of the short sidesof the crystal piece. Alternatively, three or more grooves that extendin the direction of the short sides of the crystal piece may be arrangedin the direction of the long sides of the crystal piece. As yet anotherconfiguration, for example, one wide groove may be formed between afirst end portion and a second end portion of the crystal piece, and anexcitation electrode may be formed on a bottom surface of the groove. Inthis case, the bottom surface of the groove on which the excitationelectrode is formed is a main surface of a vibration portion.

The configuration according to this embodiment may have vibrationcharacteristics generated by a full-width thickness shear mode asdescribed in the first embodiment. In this case, in addition to theoperational effects described in this embodiment, a uniform vibrationcan be obtained due to generation of a full-width thickness shearvibration as described in the first embodiment. Therefore, bettervibration characteristics can be obtained.

In the above description, configurations in which the entirety of thecrystal piece or constituent parts of the crystal piece have asubstantially rectangular parallelepiped shape have been described, butthe present invention is not limited to this configuration and can beapplied to a shape having a thickness that gradually becomes smallerfrom a central portion thereof toward end portions thereof such as abeveled structure or a convex structure, for example. In this case, thethickness T can be applied to the thickest part (for example, portion atcenter of excitation electrodes) between the excitation electrodes.

The vibration distribution of the full-width thickness shear mode in thecrystal piece in each embodiment is generated at both the front and rearsurfaces of the crystal piece.

The dimensions, shapes, directions and so forth of each of the partsdescribed above are not strictly required and the present inventionincludes equivalents thereto as understood by one skilled in the art.

The purpose of the embodiments described above is to enable easyunderstanding of the present invention and the embodiments are not to beinterpreted as limiting the present invention. The present invention canbe modified or improved without departing from the gist of the inventionand equivalents to the present invention are also included in thepresent invention. In other words, appropriate design changes made tothe embodiments by one skilled in the art are included in the scope ofthe present invention so long as the changes have the characteristics ofthe present invention. For example, the elements included in theembodiments and the arrangements, materials, conditions, shapes, sizesand so forth of the elements are not limited to those exemplified in theembodiments and can be appropriately changed. In addition, the elementsincluded in the embodiments can be combined with each other as much astechnically possible and such combined elements are also included in thescope of the present invention so long as the combined elements have thecharacteristics of the present invention.

REFERENCE SIGNS LIST

-   -   1 crystal vibrator    -   2 crystal vibrator    -   10 crystal vibration element    -   11 crystal piece    -   14 a excitation electrode    -   14 b excitation electrode    -   20 lid member    -   23 internal space    -   30 substrate    -   36 a conductive holding member    -   36 b conductive holding member    -   40 vibration region    -   50 non-vibration region

The invention claimed is:
 1. A crystal vibration element comprising: arectangular crystal piece having a prescribed crystal orientation, andhaving a first direction and a second direction in a plan view thereof,a front surface and a rear surface opposite the front surface, and athickness shear vibration is a main vibration thereof, wherein avibration distribution in the crystal piece has a vibration region thatextends in a band shape in the second direction and non-vibrationregions that are adjacent to opposed sides of the vibration region inthe first direction of the crystal piece; a first rectangular excitationelectrode on a front surface of the crystal piece; and a secondrectangular excitation electrode on a rear surface of the crystal piece,wherein respective short sides of each of the first and secondrectangular excitation electrodes are parallel to respective long sidesof the rectangular crystal piece, and wherein a relationship of a lengthEL of the respective short sides of each of the first and secondrectangular excitation electrodes to an effective thickness Te of thevibration region of the rectangular crystal piece satisfies thefollowing:Te=T+Tex·γex/γxt, andEL/Te=1.603·n−0.292, where T is a thickness of the rectangular crystalpiece in the vibration region, Tex is a total thickness of the firstrectangular excitation electrode and the second rectangular excitationelectrode, γex is a specific gravity of a material of the firstrectangular excitation electrode and the second rectangular excitationelectrode, γxt is a specific gravity of a material of the rectangularcrystal piece, and n is a natural number and is a wavenumber in thevibration region.
 2. The crystal vibration element according to claim 1,wherein a strong vibration region of the vibration region has firstdistributions having opposite phases from each other and that arelocated respectively at a first side on the front surface of the crystalpiece that extends in the first direction and at a second side on therear surface of the crystal piece that extends in the first direction.3. The crystal vibration element according to claim 2, wherein the firstdistributions each have a semi-elliptical distribution.
 4. The crystalvibration element according to claim 2, wherein the strong vibrationregion of the vibration region further has a second distribution isarranged next to the first distributions in the second direction and islocated at the front surface and the rear surface.
 5. The crystalvibration element according to claim 4, wherein the second distributionis an elliptical distribution that is elongated in the first direction.6. The crystal vibration element according to claim 2, wherein, in thevibration region, a strong vibration region of a displacement componentin a third direction perpendicular to the front surface has a thirddistribution that, with reference to a center line that extends in thesecond direction at a center point in the first direction of the crystalpiece, includes a plurality of first distributions that are on a firstside of the center line in the first direction and are arrayed in thefirst direction, and a plurality of second distributions that are on asecond side of the center line in the first direction, are arrayed inthe first direction, and have an opposite phase to the firstdistributions.
 7. The crystal vibration element according to claim 1,wherein the vibration region has a distribution that extends to opposedends of the excitation electrodes in the second direction of the crystalpiece.
 8. The crystal vibration element according to claim 1, whereinthe vibration region has a distribution that extends past opposed endsof the excitation electrodes in the second direction of the crystalpiece.
 9. The crystal vibration element according to claim 8, whereineach of the first and second excitation electrodes are spaced apart fromopposed ends of the crystal piece in the second direction.
 10. Thecrystal vibration element according to claim 1, wherein the first andsecond excitation electrodes are positioned such that a gap having adistance G is between the respective short sides of the first and secondrectangular excitation electrodes and the respective long sides of thecrystal piece, and 0<G/T≤0.5, where T is a thickness of the crystalpiece between the excitation electrodes.
 11. The crystal vibrationelement according to claim 10, wherein G/T≤0.2.
 12. The crystalvibration element according to claim 10, wherein 0.0002≤G/T.
 13. Thecrystal vibration element according to claim 10, wherein W/T≤10.2, whereW is a width of the crystal piece in the second direction.
 14. Thecrystal vibration element according to claim 1, wherein the vibrationregion has at least one strong vibration region.
 15. The crystalvibration element according to claim 1, wherein the respective longsides of the crystal piece are perpendicular to the second directionwhen the crystal piece is viewed in a plan view thereof.
 16. The crystalvibration element according to claim 1, wherein the first direction isan X axis direction of the crystal orientation of the crystal piece. 17.The crystal vibration element according to claim 1, further comprising:a frame body that surrounds an outer periphery of the crystal piece; anda connection member that connects the crystal piece and the frame bodyto each other.
 18. A crystal vibrator comprising: the crystal vibrationelement according to claim 1; a substrate; and a conductive holdingmember that supports the crystal vibration element on the substrate sothat the crystal vibration element is able to vibrate.
 19. The crystalvibrator according to claim 18, further comprising a lid bonded to thesubstrate via a bonding material such that the crystal vibration elementis provided in an internal space between the substrate and the lid. 20.A crystal vibrator comprising: the crystal vibration element accordingto claim 17; and first and second substrates bonded to the frame body atfront and rear sides thereof such that the crystal vibration element isaccommodated in an internal space therebetween and is able to vibrate.21. A crystal vibration element comprising: a crystal piece having aprescribed crystal orientation, and having a first direction and asecond direction in a plan view thereof, a front surface and a rearsurface opposite the front surface, and a thickness shear vibration is amain vibration thereof, wherein a vibration distribution in the crystalpiece has a vibration region that extends in a band shape in the seconddirection and non-vibration regions that are adjacent to opposed sidesof the vibration region in the first direction of the crystal piece; afirst excitation electrode on a front surface of the crystal piece; anda second excitation electrode on a rear surface of the crystal piece,wherein the crystal piece includes a first part that has the vibrationregion, and second parts that are adjacent to opposed ends of the firstpart in the first direction, the first and second excitation electrodesare provided in the first direction so that the crystal piece has aplurality of wavenumbers in the first direction of the vibration region,and whereinTe=T+Tex·γex/γxt, andL1/Te=1.603·n−0.292 where Te is an effective thickness, Tex is athickness of the first and second excitation electrodes, T is athickness of the crystal piece between the first and second excitationelectrodes, L1 is a length of the first part in the first direction, γexis a specific gravity of a material of the excitation electrodes, andγxt is a specific gravity of a material of the crystal piece, and n is awavenumber and a natural number.
 22. The crystal vibration elementaccording to claim 21, wherein the second parts are thinner the firstpart.
 23. The crystal vibration element according to claim 22, whereinthe crystal piece further includes third parts that are adjacent toopposed ends of the second parts in the first direction, and the thirdparts are thicker than the second parts.
 24. The crystal vibrationelement according to claim 23, wherein the third parts of the crystalpiece are the same thickness as the first part.
 25. The crystalvibration element according to claim 21, wherein the first and secondexcitation electrodes are cover the entire length of the vibrationregion in the first direction.